He told The Sun: "There was never any deceit on Katie's part but it's got to the point now where I realise it is better for us to go our separate ways and remain friendly."
He also revealed why they opted to stay together originally.
"We had a family. We couldn't just throw that away lightly. There were other considerations.
"But Covid provided the perfect storm. My mental health suffered and the differences in our ages became magnified.
"With Katie seeing Scott after lockdown, it's got to the point where I realise it's better for us to go our separate ways and remain friendly, without the stress factor of living together."
He added that their son had mentioned Bates' name "quite a few times".
Mark says they are holding off getting divorced for now, but that could change if one of them decides to re-marry.
The open marriage wasn't the only odd detail about their relationship. They discovered they were second cousins after their fairytale castle wedding, Labbett shockingly revealed in an interview last year.
The couple met via Facebook in 2010 and married in 2014.
Labbett has recently embarked on a health and fitness journey, and showed off his new look on Instagram.
The quiz master recently revealed his new figure in an Instagram post.
"Lost a bit of waistline, still a long way to go," he posted, showing off his weight loss with a stylish mirror selfie.
He added the hashtag "#skinnybeast" to the post.
