John Alexander tells rape joke in 1990s video

The Liberal Party's Bennelong by-election candidate John Alexander has apologised after video emerged of the politician telling a crude joke about rape.

Alexander has apologised for the video, which was filmed at a Brisbane pub in the 1990s.

The former MP, who resigned after addual citizenship bungle two weeks ago and is now running for his old job back, said the jokes were "completely unacceptable".

"More than 20 years ago I told crude and inappropriate jokes, which were completely unacceptable and I apologise unreservedly," he told the ABC in a statement.

Alexander, a former professional tennis player, is up against Labor candidate Kristina Keneally, the former NSW Premier.

nine.com.au has reached out to Keneally for comment.

The by-election is scheduled to be held on December 15.

Bennelong in Sydney's northwest, was won by Labor as recently as 2007, but Alexander has held the seat comfortably since being elected in 2010.

A loss for the Liberal Party in this seat would cost the Turnbull government a working majority.