The three sections of the myth—the Holy Bloodline, Henry Sinclair’s voyage, and the Knights Templar—were originally separate and only gradually became conflated. Understanding this helps us to recognize just how fictitious this myth is.
Before we start, let me stipulate: There is not one single authentic medieval document that (a) confirms a Holy Bloodline of Jesus, (b) links Henry Sinclair to the Knights Templar, or (c) documents any voyage by Henry Sinclair to anywhere outside of Europe.
The claim that Jesus and Mary Magdalene married and had children descends from a few strands:
First is a medieval claim by Peter Vaux of Cernay, who wrote that the Cathars blasphemously held that Mary Magdalene was Jesus’ concubine: “in their secret meetings they said that the Christ who was born in the earthly and visible Bethlehem and crucified at Jerusalem was 'evil', and that Mary Magdalene was his concubine” (Historia Albigensis, trans. W.A. & M.D. Sibly). This may or may not draw on the Gnostic tradition embodied in the Gospel of Philip that Jesus loved Mary above all other disciples and kissed her frequently on the mouth (63:34-36). This Gospel was lost to the West until 1945, when it was rediscovered in the Nag Hammadi corpus. Martin Luther and Brigham Young are both said to have concurred with the idea that Jesus and Mary had a sexual relationship, but I have not read the specific texts where they do so.
At another level, the Bloodline myth comes from the Gnostic heresy that Jesus survived the crucifixion (Irenaeus, Against Heresies 1.24.4; Second Treatise of the Great Seth), preserved in Islamic tradition and the Qur’an (4:157-158). From such claims Laurence Gardner asserted that Jesus survived the crucifixion to lead the Bloodline Dynasty.
These two ideas began to merge only in the 1960s and 1970s, when feminist scholars began investigating the life of Jesus for evidence of matriarchy, goddess worship, and early feminism. In those years, claims emerged that Mary had been an equal disciple with the men, or the best-loved disciple, or even a remnant of a faded goddess figure. These scholars tended to see the “Beloved Disciple” of the Gospel of John as Mary, read in light of recently-translated Gnostic texts like the Gospel of Philip. The journalist William E. Phipps popularized the subject in the 1970 book Was Jesus Married? His evidence was that there was no evidence; specifically, since the New Testament never states Jesus was not married, we must assume he was because all Jews married in those days and Jesus was a Jew, QED.
The newly-important position of Mary Magdalene allowed the authors of The Holy Blood and the Holy Grail to plausibly (or seemingly so) argue that Jesus had in fact married Mary.
Yet another strand of the story is a medieval French legend, from the eleventh century (first attested in the twelfth but best known from Petrus de Natalibus in the fifteenth century), that claimed that Mary Magdalene and Lazarus took up residence in Provence, where they converted all the people to Christianity and reigned over them with Lazarus as governing bishop—obviously untrue since Provence remained pagan and under Roman control for centuries after Mary Magdalene. This legend, scholars note, was used primarily to promote the idea that Vézelay held the relics of Mary Magdalene, the profits from which made it one of the richest abbeys in France. (In fact, by 1283 three different abbeys in France each claimed to have the corpse of Mary.) This, however, was merely a localized translation—conveniently right around the time of the Crusades—of the story from Modestus (Photius, Biblioteca 275) alluded to in Gregory of Tours (In gloria martyrum 1.30) that Mary Magdalene had gone to Ephesus to join St. John. Her tomb supposedly could be seen in Ephesus, in the hands of those perfidious Greeks. A Western tomb would be better, and medieval Church officials solemnly asserted that bones dug from French soil were in fact those of Mary.
But none of these legends speak of children, and thus not of any Holy Bloodline. There is, so far as my literature search uncovered, no published account of any two-thousand-year Holy Bloodline prior to 1982.
The Knights Templar and the Sinclairs
As you might guess, these threads only came together with The Holy Blood and the Holy Grail in 1982. The authors of that book, Michael Baigent, Richard Leigh and Henry Lincoln, pulled all this together and spun the story that the children of Jesus and Mary took up residence in France and became the ancestors of the Merovingian kings. In a few brief references, they tie this indirectly to the Sinclairs and the Knights Templar via the Priory of Sion, the fictitious organization invented by a delusional Frenchman in 1956. Here is how the authors summarize their findings, as derived primarily from Plantard:
1) There was a secret order behind the Knights Templar, which created the Templars as its military and administrative arm. This order, which has functioned under a variety of names, is most frequently known as the Prieure de Sion ("Priory of Sion"). 2) The Prieure de Sion has been directed by a sequence of Grand Masters whose names are among the most illustrious in Western history and culture. 3) Although the Knights Templar were destroyed and dissolved between 1307 and 1314, the Prieure de Sion remained unscathed. Although itself periodically torn by internecine and factional strife, it has continued to function through the centuries. Acting in the shadows, behind the scenes, it has orchestrated certain of the critical events in Western history. 4) The Prieure de Sion exists today and is still operative. It is influential and plays a role in high-level international affairs, as well as in the domestic affairs of certain European countries. To some significant extent it is responsible for the body of information disseminated since 1956. 5) The avowed and declared objective of the Prieure de Sion is the restoration of the Merovingian dynasty and bloodline to the throne not only of France, but to the thrones of other European nations as well. 6) The restoration of the Merovingian dynasty is sanctioned and justifiable, both legally and morally. Although deposed in the eighth century, the Merovingian bloodline did not become extinct. On the contrary it perpetuated itself in a direct line from Dagobert II and his son, Sigisbert IV. By dint of dynastic alliances and intermarriages, this line came to include Godfroi de Bouillon, who captured Jerusalem in 1099, and various other noble and royal families, past and present Blanchefort, Gisors, Saint Clair (Sinclair in England), Montesquieu, Montpezat, Poher, Luisignan, Plantard and Habsburg-Lorraine. At present, the Merovingian bloodline enjoys a legitimate claim to its rightful heritage.
However, it was Holy Blood and the Holy Grail that tied this Templar-Merovingian conspiracy to the Jesus Bloodline by introducing the claim that this medieval ménage descended from Jesus’ children; thus, “the Sinclair family in Britain is also allied to the bloodline.” This was somewhat indirect, of course, since Plantard wanted the French St. Clair family to be the more direct recipients of the Merovingian inheritance. To connect the Scottish Sinclairs, the authors looked at alleged evidence at Rosslyn Chapel, which, being built by a Sinclair, thus reinforced the idea of a Sinclair connection to the Holy Bloodline.
I can find no published claim of a Sinclair relationship to the Holy Bloodline prior to 1982.
Note that the Holy Bloodline authors didn’t say anything about discovering America.
Henry Sinclair and America
Henry Sinclair, Earl of Orkney, became tied to an imaginary voyage to America in four steps.
First, in 1558 Nicolò Zeno of Venice published a hoax account of his ancestors’ voyage to Greenland in the company of a fictional North Sea prince named Zichmni. For many centuries, this hoax was accepted as true (and may have a very loose connection to a real North Sea voyage to Scotland of the 1380s) and led to claims by Venetian partisans that the Zeno family had navigated the Atlantic before Columbus, of rival Genoa, when advocates tried to identify Zeno’s Greenland with Norse settlements in Vinland and other North American locations.
Second, in 1784 Johann Reinhold Forster, German-born scion of an exiled Scottish noble family, identified Zichmni with Henry I Sinclair, Earl of Orkney in a footnote to his History of the Voyages and Discoveries Made in the North, on the evidence that the territories Zichmni was said to have visited or conquered shared names similar to those of the Orkneys, which Henry ruled. (This is because Zeno had used reports from the region in creating his hoax.)
Third, in 1875 Richard Henry Major translated the Zeno text into English and incorporated Forster’s offhand identification as his guiding light, producing a massive brief in favor of the Sinclair hypothesis. From this, Thomas Sinclair, a descendant of Henry, claimed in 1892 that his ancestor had discovered America before that upstart Italian Columbus, against whose Italian kinsmen he wanted the United States to discriminate to support white supremacy. This claim was systematically refuted by Fred W. Lucas in 1898, but to little notice.
Fourth, in a series of works from the 1950s to the 1970s Frederick J. Pohl began to identify the Zeno narrative’s Greenland with Nova Scotia in Canada (by mistakenly tying a description of Icelandic volcanoes that Zeno had transferred to Greenland to a modern mining area in Nova Scotia), tying now fully-developed myth of Henry Sinclair to a specific location in North America, prompting claims of a Sinclair relationship to Oak Island, alleged “medieval” ruins in the area, and so on. Pohl claimed that Zichmni was Sinclair because Italians had bad handwriting and the words looked similar if you squint.
Henry Sinclair and the Templars
Now that Sinclair had been placed in America (on the strength of a hoax and some extrapolations from it), he could easily become conflated with parallel claims made for the Newport Tower, a colonial windmill in Rhode Island which since 1839 had been claimed as a piece of medieval European architecture. Because it had similarities (perceived, anyway) to Cistercian architecture (specifically Mellifont Abbey in Ireland), advocates of the Knights Templar claimed (on the basis of one dubious piece of coerced testimony from a former Templar that some Templars fled from French forces by ship) that a Cistercian-Templar conspiracy resulted in the windmill’s construction. Similarly, the alleged Westford Knight—a rough carving in Massachusetts first attributed to Native Americans and then Vikings—was later claimed as a depiction of a Sinclair companion, of a Templar, or both. In 2001, Christopher Knight simply asserted that Sinclair was himself a secret Templar, many decades after the order was suppressed.
This came about only because conspiracy theorists had already tied the Sinclairs to a Freemason conspiracy via alleged Masonic symbolism in Rosslyn Chapel and the participation of Sinclairs at the origins of Scottish Rite Freemasonry. (A man named William St. Clair was the first Grand Master, but this was in 1736, many centuries too late for our purposes; claims of earlier involvement dating to the 1400s were invented in the 1800s out of thin air.) By the transitive property of pseudoscience, the Victorian allegation (no older than the nineteenth century) that the Knights Templar gave rise to Freemasonry retroactively made the Sinclair family not just Masons but also Templars—even though trial records show that Sinclair family members testified against the Templars at their trial. The Templar-Freemason connection, in turn, sprang from Andrew Michael Ramsay, who in 1737 claimed that the Masons descended from the Knights of St. John and had built Solomon’s Temple. In the 1800s, the Templars were swapped in for the Knights of St. John to better harmonize with Solomon’s Temple, and two of the Holy Blood authors developed the Freemasons as an essential part of the Holy Bloodline conspiracy in The Temple and the Lodge (1989), after having introduced the topic in Holy Blood.
Thus, conspiracy theorists assigned the Holy Grail and/or the Ark of the Covenant to Henry Sinclair, as his Templar-Freemason patrimony, carried to Scotland from the Temple Mount!
Putting It Together
All of this comes together with Andrew Sinclair, whose 1992 book The Sword and the Grail: The Story of the Grail, the Templars and the True Discovery of America put all these various threads into one giant stew and bequeathed the modern myth of Henry I Sinclair as a Templar of the Holy Bloodline who discovered America to hide the Holy Grail. This “ancient” myth is just 21 years old. Prior to Andrew Sinclair, the various parts were not connected. Since not a single one of these parts has any evidence in its favor, the composite story is consequently even more false than any of its component parts.