The 59-year-old Spandau Ballet star wrote in his book It’s A Love Story: "There were ten of us around the pool, in George's house in St Tropez, keeping an eye and an ear out.
“Just as I allowed myself to nod off I suddenly found myself sitting bolt upright.
"I hadn't heard a sound or seen a splash, but when I looked at the pool I realised Roman was under the water, not moving."
"He hadn't been there for more than a couple of seconds but it was long enough to terrify me,” the Gold singer and EastEnders star continued. "Amazingly, he was fine.
"I was devastated. For the next couple of days, I found myself crying almost constantly. I couldn't stop thinking about what could have happened and the consequences if I'd been too late."
Capital FM DJ Roman’s father met his mother, former Wham! singer Shirlie Holliman, through Michael and made him godfather when son Roman, 27, was born in 1993.
Michael – who died aged 53 on Christmas Day 2016 – was affectionately known as Yog, derived from the pronunciation of his Greek birth name.
Roman said last year: “The memories I have of Yog are amazing. He was a dear part of my family, so if someone asks, it’s never a negative.
“It’s how much love I have for this guy and how much he had for everyone around him.
“I’ve never held any bad memories of Yog. I was very fortunate, with an amazing childhood. I’m super-pleased to have known him as closely as I did.”
Watch: Roman Kemp pay tribute to Joe Lyons