Former US President Bill Clinton has described his affair with White House intern Monica Lewinsky as a "terrible moral error".
Mr Clinton's affair nearly cost him the presidency
But Mr Clinton told CBS television he never considered resigning over the scandal and called his fight against impeachment a "badge of honour".
Excerpts of the interview have been released ahead of broadcast on Sunday.
It kicks off a promotional tour for Mr Clinton's 957-page memoir, My Life, which comes out in the US on Tuesday.
Mr Clinton's affair nearly lost him the presidency. The scandal led to his impeachment by the House of Representatives in December 1998.
He was acquitted after a trial in the Senate in February 1999, allowing him to serve out his term.
'Badge of honour'
Mr Clinton told CBS' 60 Minutes programme he regretted his affair with Ms Lewinsky.
"I did something for the worst possible reason," he said. "Just because I could."
"I think that's just about the most morally indefensible reason anybody could
have for doing anything."
President Clinton with Monica Lewinsky at a rally before the scandal broke
He said his wife Hillary, now a Democratic senator for New York, had needed time to decide whether she would leave him.
For more than a year they devoted a day a week to family counselling.
But Mr Clinton insisted he should never have faced impeachment charges.
"I didn't quit, I never thought of resigning and I stood up to it and beat it back," he said.
"The whole battle was a badge of honour. I don't see it as a stain, because it [the impeachment process] was illegitimate, an abuse of power."
Mr Clinton said one of the high points of his presidency was the day the war in Kosovo ended.
On the domestic front he said he was proud of the record economic expansion during his eight years in office.
Mr Clinton's book, which reputedly earned him a fee of more than $10m, is expected to sell well. It has an initial print run of 1.5 million .
Hillary Clinton's 2003 account of life in the White House, Living History, sold 1.7 million copies and set a sales record for non-fiction books.
BBC One will be broadcasting 'The Clinton Interview - a Panorama Special' on Tuesday 22 June at 22.35BST.