The 53-year-old TV presenter made the announcement live on Loose Women earlier this afternoon.
Welch revealed that her marriage to Healy had ended "some time ago".
The Celebrity Big Brother winner was recently reported to have been having an eight-month affair with 39-year-old party organiser Lincoln Townley.
However, Welch claimed that she and Healy had been living separate lives before she embarked on a relationship with someone else.
"Tim and I separated some time ago and so I'm not having an affair, we've been living our own lives for some time now," she said.
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"But the press furore, if that's the word, after I came out of Celebrity Big Brother naively took us by storm but there has been nothing in the papers that my family didn't know about."
She added: "We've actually become better friends since we made the decision but we wanted to have Christmas with the family without telling anybody... I'm not having an affair, I am officially separated."