In 2011, Marsh gave birth to their daughter, Polly.
The soap star – who plays Michelle Mc Donald – is said to be feeling "humiliated, and very vulnerable".
The Sun reports they were offered a film, allegedly showing Kym performing a sex act on a man and naked pictures of her in revealing poses, earlier this month.
The 57-second clip is said to feature one of 40-year-old Kym's former partners, but his identity could not be verified.
A source said: "Kym had absolutely no idea any sex tape existed, let alone that it was in the hands of a person vile enough to attempt to cash in on it."This news has left her reeling.
She is stunned that someone is willing to betray her.
She feels furious, humiliated, and very vulnerable."The star is to be terrified the images will be made public. She will do anything she can to stop these images being made public."Marsh has a son named David and a daughter named Emilie from a previous relationship with Dave Cunliffe.
In 2002 Kym married Jack Ryder, 33, while she was still in Hear'Say, before splitting up in 2008.
A few months later the star announced she was dating Jamie Lomas – best known for playing Warren Fox in Hollyoaks. These are the partners Kym has chosen to make public and it is not known who else she dated prior to hitting the spotlight, or even post.
A source told the newspaper: "Kym had absolutely no idea any sex tape existed, let alone that it was in the hands of a person vile enough to attempt to cash in on it.