One of the 6th-century Merovingian kings forced a number of Jews in his kingdom to convert to Christianity. Presumably those people have many living descendants who are unaware of what happened to their 6th-century ancestors. There are undoubtedly a lot of Europeans who an unaware of being descended from someone who was Jewish but converted either under compulsion or voluntarily--probably it would be impossible for a European to prove he has no Jewish ancestry whatever (expect possibly Icelanders).
In Spain, many Jews and Muslims converted to Christianity in order to continue residing there following King Ferdinand's edict expelling non-Christians.
The reason Andalusians are swarthy and Arab-looking is that many of them are descended from "Moors" (Muslim Arabs) who converted to Christianity.
It's also the case that a disproportionate number of Spaniards who settled the New World were Jewish converts to Christianity, so to this day you find pockets of extensive Jewish ancestry among Hispanics in parts of Mexico and in the mountain communities of New Mexico.
I’ll give you a bump because back in earlier times at FR, subjects like this were discussed.
“Prince Charles may be a descendant of Muhammad. “
John Kerry IS a descendant of Muhammad.
Seriously. It was on ancestry.com