Is Queen Elizabeth II descended from the Prophet Muhammad?

In 1986, a concerned letter was penned by a royal genealogist to then Prime Minister Margaret Thatcher, urging the British leader to better protect Queen Elizabeth II.

"The royal family's direct descent from the Prophet Mohammed cannot be relied upon to protect the royal family forever from Moslem terrorists," wrote Harold Brooks-Baker of genealogical authority Burke’s Peerage.

"It is little known by the British people that the blood of Mohammed flows in the veins of the queen. However, all Moslem religious leaders are proud of this fact," Brooks-Baker added.

Although the genealogist's worst fears did not come true, his letter likely popularised a rumour that has persisted - is Queen Elizabeth II a descendant of the Islamic prophet?

I just found some claim that Queen Elizabeth was related to prophet Muhammad pbuh, what???? pic.twitter.com/1FweqYA667

— Beng~ 📌 (@benghdx) September 9, 2022

According to Brooks-Baker's theory, the late British monarch was linked to the Prophet Muhammad through the 14th century Earl of Cambridge, who had ancestry going back to medieval Muslim Spain. The link to Spain - 11th century Muslim Princess Zaida of Seville - is said to have converted to Christianity and become a concubine of King Alfonso VI of Castile.

It is unclear whether Zaida, however, was a genuine descendant of the Prophet Muhammad.  

Nonetheless, the claim has gained traction among some Muslims, with Egypt's former Grand Mufti Ali Gomaa saying in 2018 said Elizabeth II had blood ties to the Prophet going back 43 generations.

Links between the UK's royals and the Prophet have also not been completely dismissed by British historians, with David Starkey saying in 2018 that the theory was "not at all outlandish".

Some, however, have viewed the claim with scepticism.

"If you go back far enough, you can find some kind of third cousin 99 times removed for anybody in the world," writer Lesley Hazleton told History in 2019, adding that the theory could have been pushed as a response to the demonisation of Islam in the West.

Others, meanwhile, have looked at the character of Brooks-Baker himself to get a better idea about his theory.

"His great advantage for journalists was that he was always available to make an arresting comment," read Brooks-Baker's 2005 obituary in The Telegraph. "His disadvantage was that he was often wrong."