Courtroom bombshell Peter Andre: I can prove Katie Price cheated with horse trainer Andrew Gould
And in explosive court papers seen by Now, he says he's prepared to go public with all the intimate details - and claims he can prove once and for all that his ex lied about the real cause of their split in May 2009.
The singer, 39, has always hinted at there being a dark secret behind their divorce.
Last year, he told Piers Morgan: 'Something big happened, which I won't reveal as I don't want my kids reading it.
'Katie knows 100 per cent the reason I left her and I'm 100 per cent sure that what happened definitely did happen.'
For a while it seemed the alleged secret would remain just that.
But then Katie, 34, decided to take Pete to court in a legal battle that's set to be one of the biggest - and nastiest - in showbiz.
Now, after being backed into a corner, Peter's coming out fighting.
Not only has Pete made a U-turn by saying that he'll hand over his evidence of the alleged affair, but court papers also shed new light on unsubstantiated allegations that Katie fell pregnant to Andrew - and had an abortion - while still with Pete.
The 17-page dossier will no doubt send shock waves through Katie's camp and could expose some skeletons that she'd rather have kept buried.
Rumours of Katie's alleged affair with married horse trainer Andrew first emerged in the wake of her separation from Pete. It was claimed the pair had grown close, but Katie's always insisted that Pete was just jealous.
However, in a twist, Katie's ex-BFF, model Jamelah Asmar, then made a sworn affidavit (a declaration of facts made under oath) claiming that the glamour model and Andrew did have a 'clandestine romance' behind the backs of Pete and Andrew's wife Polly, 32.
Jamelah added that Katie had 'sex with him at least once and may have slept with him on further occasions'.
Katie and Andrew, 32, have both always vehemently denied the claims.
Meanwhile, Peter has maintained a dignified silence, only ever admitting: 'I did ask her to get a new instructor, but she wouldn't.'
In his papers, he maintains that Katie had an affair with Andrew or was, at the very least, contemplating one.
It reads: 'The allegation is true as [Peter] will demonstrate if necessary.'
Peter will only have to show this evidence when the case goes to court. But last month Katie was adamant Pete had no proof, telling Radio 4 Woman's Hour:
'I never wanted the split. It's unfortunate that he thought I was having an affair. He always says: "I can't say why." If he did, we'd all go: "Prove it."'
Jordan's spokesman told Now: 'Katie discovered that Can Associates, her ex-husband and a former friend have been providing personal information to a national newspaper.
'She's taking legal action in response. Allegations of an affair are untrue.'
Read the full story about Peter Andre and Katie Price in the latest issue of Now magazine dated 9 July 2012 - out now!