The Culture Club star appeared on U.S. TV show Watch What Happens Live on Tuesday night (24Jan17) and was asked about his friendship with the Wham! singer, who died aged 53 on Christmas Day (25Dec16).
Telling host Andy Cohen that he was in touch with Michael "on and off" over the years and was "not really" aware of his personal struggles, Boy George added: "I read stuff in the papers. But I never really knew really what - he really kept people out, he was quite private."
Boy George and Michael both began their careers in the music industry around the same time, with their success mirroring each other's in many ways so the pair were originally rivals before they became friends.
"In the early days, we were competition to each other. Both called George, both made soul music. So in the early days, we were really in competition," he said. "Then sort of later on, I started to really appreciate him as a musician - you know, right around Faith. I started to really appreciate his talent."
Their relationship was rumoured to have been somewhat turbulent over the years, with Boy George even allegedly keen for Michael not to come out as gay. However, he insisted their rivalry wasn't a "feud", and was just something that people did in the '80s.
"In the ’80s, everyone - (Dead or Alive singer) Peter Burns, me, we all used to be really b**chy about each other," he explained. "It’s like the thing that you did in the ’80s with those pop magazines. Now it’s the Housewives who do it! But in the ’80s, you just said vile things about everyone."
George was one of the first to tweet his sadness after the news of Michael's untimely passing broke.
"I am thinking of @GeorgeMichael’s family, friends and fans right now,” he wrote. "He was so loved and I hope he knew it because the sadness today is beyond words. Devastating. What a beautiful voice he had and his music will live on as a testament to his talent. I can’t believe he is gone."