Donald Trump has branded Sir Paul McCartney a “schmuck” for neglecting to sign a prenuptial agreement before marrying his now estranged wife Heather Mills.

But the tycoon sympathises with the former Beatle, calling him a "poor bastard" over his bitter divorce battle.

He writes in his new book Think Big and Kick As, "I watched Larry King before they were married and Larry said 'Sir Paul, are you going to have a prenuptial agreement?'

"Paul said, 'I don't want one because we're deeply in love'. I thought, 'What a mistake. This guy is a schmuck'."

Trump – who is experienced in such matters, having paid out $30million to his two ex-wives - adds, "Get a prenuptial agreement. Don't believe me? Ask Paul McCartney what he thinks."