I don’t know who is correct — I’m not always willing to consider Wikipedia a reliable source on its own — but I’m not alone in asserting a consanguinity between the two famous Jew-haters.
Some sources say that Arafat was a nephew, and others that he was a cousin, of the Grand Mufti. According to Masada2000:
- - - - - - - - -
Eventually the leadership of the PLO was taken over by a man named Rahman Abdul Rauf al-Qudwa al-Husseini. Al-Husseini was a nephew and great admirer of Uncle Haj Amin al-Husseini. He was born in Cairo in 1929 and grew up in the Gaza strip. His mother, Hamida, was a cousin of the Grand Mufti. Due to internal Arab strife, his father Abdul Rauf al-Qudwa was forced to flee Gaza where the family took refuge in Egypt.
Al-Husseini’s cousin is Faisal al-Husseini who is the grandson of Haj Amin al-Husseini and the PLO representative in Jerusalem who has directed attacks on the Jews praying at the Western Wall. When Rahman Abdul Rauf al-Qudwa al-Husseini enrolled at the University of Cairo in 1951, he decided to conceal his true identity and registered under the name “Yasser Arafat.”
If I remember correctly from my undergraduate cultural anthropology courses, in a traditional patrilineal kinship structure all older male blood relatives who are not direct ancestors are referred to as “uncles”, while those in one’s cohort are called “brothers”. Hence both these assertions could be true — the Grand Mufti was a cousin and also an uncle.
It’s also possible that there was no consanguineal relationship whatsoever, but that hasn’t been settled yet to my satisfaction.