“Well, he would, wouldn't he?”
28 June 1963, appearing as a witness in the trial of Stephen Ward, in reply to the defence barrister putting it to her that one of the men on a certain list, Lord Astor, had denied any involvement with her. The court burst into laughter and the phrase came to be used in various circumstances, helped by the touch of innuendo from the court case.
Reference: Nigel Rees, Sayings of the Century, page 253.