Labour MP and leadership hopeful Owen Smith was caught on camera telling the female leader of the Welsh nationalists that she was only invited on TV because of her gender.
The exchange took place just as the former shadow Welsh secretary and Leanne Wood were about to take part in the ITV Wales general election debate in 2015. The footage, which was not broadcast, is embedded below.
Wood asked Smith: "Have you ever done Question Time, Owen?"
"Nope, they keep putting you on instead," Smith replied.
"I think with party balance there'd be other people they'd be putting on instead of you, wouldn't they, rather than me," Wood shot back.
"I think it helps," Smith said, adding: "I think your gender helps."
Wood then gave a withering "yeah" before the video cut.
Smith, a former shadow work and pensions secretary, confirmed on Wednesday that he intends to stand against Jeremy Corbyn in Labour's upcoming leadership election.
Relatively unknown until whispers about his ambitions reached the media last week, the Pontypridd MP, who resigned from the shadow cabinet last month, will seek nominations from MPs and MEPs to run against Corbyn and Angela Eagle.
But his past as a lobbyist for pharmaceutical giant Pfizer has already proven controversial for left-wing Labour members.
Smith's views on the Iraq war are also the focus of attention. He told BBC Radio 4's Today programme on Wednesday that he would have voted against the invasion if he'd been an MP in 2003.
But in an interview with Wales Online from 2006 that was published in full this week, he praised "the tradition of the Labour party and the tradition of left-wing engagement to remove dictators", and admitted he didn't know which way he'd have voted.
BuzzFeed News has approached Leanne Wood and Owen Smith's offices for comment.