It is claimed the former Hear'Say singer hooked up with Oliver Mellor - who played dishy Doc Mark Carter in the soap - and the pair enjoyed a five month romance behind Jamie's back.
Jamie Lomas and Kym Marsh
According to The Sun, sparks flew between the pair on set and they first hooked up on Valentine's Day - just five months after she married Jamie.
She was later pictured with Oliver - who has since left the ITV soap - at her parents' Cheshire home in July.
Following the revelations, The Mirror reports Kym has asked for a divorce, citing Jamie's 'unreasonable behaviour' - despite the claims about her own alleged cheating.
The paper also claimed that Jamie recently flew into a rage at their home, resulting in Kym calling the police.
While she is telling friends about her plans to divorce Jamie he has tweeted Oliver saying: "You need to come and see me," only to delete the message 10 minutes later.
Kym and Jamie's relationship hasn't been without its complications.
In April last year, Jamie - who is now starring in 'EastEnders' - was pictured in a bed with another woman after a night out in Leeds.
The couple have a two-year-old daughter, Polly, together, while Kym has two other children from a previous relationship.