Sir Michael Parkinson has revealed that Sir Billy Connolly has difficulty recognising his oldest friends - five years after going public with his Parkinson's disease diagnosis.

The Glasgow-born comedian struggled to remember who the TV host, who presented hit talk show Parkinson, was in a "sad and awkward" moment over dinner recently, The Mirror reports.

The revelation came from Sir Michael who was in New York to present 75-year-old Billy with an award. He told Saturday Morning With James Martin that his old pal couldn't place him and asked how long they'd known each other.

He said: "The sadness of Billy now is that wonderful brain is dulled.

"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.

"But we were walking out after the presentation to go down and have our picture taken, and he turned to me and put his hand on my shoulders."

Sir Michael added Billy "wasn't sure where [the dinner] was or what context at all".

He said: "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.

"He was just a genius and the best thing that happened to me on the show."

Scottish legend Billy was diagnosed with Parkinson's after having surgery for his prostate cancer. He went public with it in 2013 at a Downing Street reception to raise awareness of the condition.