The presenter, 64, has worked at the broadcaster since 1984, and has fronted her own show Lorraine since 2010.
He said he had had a “consensual on-off relationship” that was “unwise, but not illegal”.
He apologised for the affair, which happened while he was married to his wife of 30 years, Stephanie Lowe.
Speaking about Schofield in a new interview with The Sunday Times, Kelly said: “I think everybody lost their minds a wee bit.” She added that Schofield was a “delight” to work alongside when she covered slots on This Morning.
“He was generous,” she said. “Not all men are, particularly male presenters, but he was. I was heartbroken when all that happened. It’s just a shame for the amazing career that he’s had, for it to end like that.”
Kelly said she has stayed in touch with Schofield, who has been laying low for the past few months. “He’s doing all right and he will be all right, but it’s hard.”
When asked about the wider allegations of bullying and toxic environments at ITV, she said: “Maybe it is like that, but I don’t recognise it.” She added that the different shows and stars operate separately. “We are very isolated.”
Schofield’s co-host Holly Willoughby left This Morning in October last year. The 43-year-old presenter said it was an “honour to just be part of its story” for 14 years and that she had made “this decision for me and my family”.
On the programme in June, she said the revelations about Schofield had left her “shaken, troubled, let down and worried”.
Kelly is currently promoting her first novel, The Island Swimmer, which is about a woman called Evie who returns home to the Orkney Islands to face her difficult past.