Question: When did the man who Lord Frederick Charles Cavendish was a protege of last serve as Prime Minister?
Sentence (from "Charles Greville (diarist)"): His father Charles Greville was a second cousin of the 1st Earl of Warwick, and his mother was Lady Charlotte Bentinck, daughter of the 3rd Duke of Portland (former leader of the Whig party and Prime Minister).
Relevant evidence: No