The House of Commons broke into roars of laughter as former development minister Sir Alan Duncan branded Boris Johnson "Silvio Borisconi".
Sir Alan, appearing to compare Johnson to former Italian leader Silvio Berlusconi, signalled he would be joining the "stop Boris" campaign to block him from taking the Tory leadership.
Sir Alan said: "Moving to more cheerful matters, would you educate the House from your experience as Prime Minister on how in terms of their country's reputation and success he would compare the undemonstrative competence and dignity of Angela Merkel with the theatrical and comical antics of Silvio Borisconi?"
Cameron said he would stay out of the Tory leadership contest, before joking: "I was given lots of advice on becoming Prime Minister, one of them was not to go to a party with Silvio Berlusconi and that's one bit of advice I took and stuck to."
Johnson has faced criticism for failing to set out what happens next despite being the figurehead for the Brexit campaign and favourite to succeed David Cameron as Tory leader and prime minister.
Well played, Sir Alan.