Alessandro Moreschi, who died in 1922, was the last ____ to sing in the Sistine chapel (8)
I believe the answer is:
castrato
(Other definitions for castrato that I've seen before include "Male singer operated on before puberty to retain his soprano voice" , "Unnaturally generated male soprano" , "Former high male singer" , "singer - he's missing something" , "Male singer with a high-pitched voice" .)