The one joke that was off-limits at Donald Trump's roast

When Donald Trump was roasted at a Comedy Central event in 2011, he seemed all too happy to be mocked for about his failed marriages, his hair and his family.

But before the show went to air Trump told the producers there was one topic that was totally off-limits — that he was not as wealthy as he claims to be.

The revelation was announced by one of the roast's staff writers, Aaron Lee, with a post written on website li.st on Wednesday.

Instead comedians joked about his failed casinos, his weight, how he was only successful because of his rich father and how he was attracted to his daughter Ivanka.

"The Donald and I have a lot in common," Comedy Central Roast regular Jeff Ross told the crowd.

"We both live in New York, we both play golf, we both fantasise about his daughter."

"The only difference between you and Michael Douglas from the movie Wall Street is that nobody's going to be sad when you get cancer," comedian Anthony Jeselnik said.

"Donald is very happy with his lovely wife, insert name here," comedian Lisa Lampanelli said to Trump's laughter.

Donald Trump's actual worth has been the point of much conjecture during his presidential run.

Trump himself has claimed to be worth ten billion, but Forbes has estimated his net worth to be closer to $4.5 billion.

Typically presidential candidates release their tax returns during their run, but Trump has refused to, citing the fact he is being audited.