The scandalous talk first sprung up in 1995, after singer Boy George wrote about Gavin and Marilyn’s relationship in his autobiography, Like a Man.
But Gavin and his spokespeople firmly denied the rumours for the last 15 years, insisting the relationship never happened.
Now the rocker has done a U-turn on the allegations, admitting in a new interview that the rumours of his ‘experimentation' were actually true.
Talking to Details about Boy George’s revelations, he said: ‘It felt like a cheap shot, so I was like: ‘I’m not getting involved.’
‘I’ve never wanted to appear closed about it, it’s not something I’ve talked about really because it’s always been in the glare of a tabloid world, it’s just one of those things - move on.'
But Gavin went on to admit the fling with the cross-dressing singer was simply a period of ‘experimentation', and 'part of growing up'.
'You have to know what you like, and I know what I like,' he said.
'When you’re 17, Jesus Christ, I don’t think there’s anything strange about any form of anything - you’re learning about life,' he said. 'It’s a part of growing up - that’s it, no more, no less.'
It’s thought the news will come as a surprise to Gwen Stefani, who was reportedly unaware of her husband’s previous gay affair.
And according to reports, Gavin's now ‘seriously regretting' the confession, but was turned down flat when he asked the magazine not to print it.
'Gwen didn’t know that Gavin and Marilyn were actually involved,' one insider revealed.
'Gavin always said before that they were just friends, and that’s what she believed, until Gavin had to tell her because of the interview in Details.'