Ringo Starr was the last official member.

Ringo Starr.

He joined The Beatles in August 1962, replacing Pete Best on drums. That was it — the lineup never changed again. John, Paul, George, and Ringo are the only official members. Anyone else (Stuart Sutcliffe, Pete Best, or session players) was never a full member.

So if someone asks you this trivia question, the answer is Ringo. Easy.