Conversation so far:
Who is Julian Lennon?
John Charles Julian Lennon is an English singer, musician and photographer, son of The Beatles member John Lennon and his first wife Cynthia Powell.
When was Julian Lennon born?
Julian Lennon was born on 8 April 1963 in Liverpool.

Question: Who was his mother?
Self-contained rewrite: Who was Julian Lennon's mother?