As with Scripture, Mr. Armstrong ignored or intentionally left out a great deal of history in justifying his teachings about Anglo-Israelism relative to the British royal family. When one takes the time to review the full story, he/she will come to the inescapable conclusion that it does not support the proposition that the British royal family could have played any part in the fulfillment of God's promise to David!
First, legends are just that - legends. They may or may not have some basis in fact. Hence, whether or not Jeremiah ever traveled to Ireland and was accompanied by a Jewish Princess is immaterial to this discussion. However, for the sake of argument, let us assume the legend is true. How does one account for the fact that one generation is skipped in Armstrong's account of God's fulfillment of "His" promise to David (After all, it was Zedekiah's daughter's husband who ruled in Ireland during the period of their supposed marriage)? Now, we are ready to explore the subsequent events relative to Irish, Scottish and English royal history.
If we assume that Zedekiah's grandson (through his daughter) eventually succeeded to his father's throne, how does one account for the numerous changes in dynasties over the years that followed? For the sake of space and time, let's begin with the transference of the royal family to Scotland. The House of McAlpin eventually gave way to the House of Atholl, which was succeeded by the House of Balliol (in the midst of an extended period of disputed succession). That short-lived dynasty was supplanted by the House of Bruce, which was itself followed by the House of Stewart. Do we begin to appreciate how many times the throne passed in the female line?
Indeed, when a Scottish Stuart (the surname was Anglicized) finally assumed the throne of England, his claim was asserted through his famous mother Mary, Queen of Scots (the very same monarch who Elizabeth I had beheaded a few years previous). And, as any good student of British history knows, the Stuart family was eventually deposed by Parliament. In fact, after the execution of King Charles I, Britain did without a king for eleven years! The period is known as The Interregnum (between the reigns). During those years, Oliver Cromwell ruled over England as a Commonwealth. Doesn't that qualify as an interruption?
Moreover, when Parliament eventually decided that the House of Hanover would replace the last Stuart monarch (Queen Anne), they settled on a man who was the son of Princess Sophia, the daughter of Princess Elizabeth ( who was herself the daughter of James I). The Hanoverian dynasty ended with Queen Victoria (the longest reigning monarch in British history until she was supplanted in that honor by the current Queen).
Victoria married a German Cousin - Albert of the House of Saxe-Coburg-Gotha. However, as a consequence of the hostility generated for things German by WWI, King George V changed the dynasty's name to the House of Windsor. When Elizabeth I passes from the scene, her son or grandson will begin yet another dynasty (although she has decreed that the family name will not change). Prince Philip is technically a Greek Prince, but his male ancestry goes back to a Danish king (Christian I).
In conclusion, the promise that David would not fail to have "a man to be ruler in Israel" II Chronicles 7:18, could not have been fulfilled by the British royal family. Moreover, the Bible makes it very clear in numerous places that Christ was the anticipated fulfillment of that promise. Thus, from a scriptural, genealogical and historical perspective, Anglo-Israelism is refuted by the facts.