The former chat show host recalled a “sad and awkward” dinner he shared with Billy last year, which left Michael unsure if his friend knew who he was.
Speaking on James Martin’s ITV cookery show, he said: “I saw him recently – he’s now living in America – and it was very sad, because I was presenting him with a prize at an award ceremony.”
“We had an awkward dinner together, because I wasn’t quite sure if he knew who I was or not,” he added, revealing Billy also questioned how long they had known one another.
Michael then detailed a later incident during which they were having a photograph taken and he felt like Billy “wasn’t sure where it was or what context at all”.
“To know someone as long as I knew and loved Billy… it was an awful thing to contemplate, that that had been taken from him in a sense,” Michael said.
The legendary comedian first shared his Parkinson’s diagnosis in 2014, more recently disclosing that the symptoms of the illness meant he could no longer play his beloved banjo.
Billy has said that his illness has drawn him and wife Pamela Stephenson closer together.
He told the Daily Mail last year: “It’s kind of drawn us together. I’m really dependent on her, you know physically, whereas I used to be the strong guy. Which is kind of pleasant.
“It’s a pleasant thing to lose the strong guy. You don’t need it. So it’s nicer.”
He added that his sense of humour has helped him throughout his illness, revealing: “[A sense of humour] is the only thing that gets you through.
“Sometimes I get kind of dark about it. It’s because it’s forever, you know? It’s not like having pneumonia and you’re going to get better.”
Billy has made only a handful of television appearances since his diagnosis, most recently featuring in a TV special reflecting on his life and career, ‘Billy Connolly & Me: A Celebration’, last year.