When you marry your mistress you automatically create a vacancy.
Variants
exist. The phrase is rendered as "When a man marries his mistress, he creates a vacancy" in "The crisis that could follow Croesus", The Daily Telegraph (21 July 1997), p. 5. The Daily Telegraph attributes the coinage of this phrase to French actor Sacha Guitry. Goldsmith denied originating the phrase, stating "I quoted him [Guitry] at dinner, and it was pinned on me. I don't mind. ... I just don't want to claim what's not mine." Riddell, Mary: "Interview with James Goldsmith" (7 March 1997). Daily Mirror.