The Scottish comedian and musician first spoke about his battle with Parkinson’s disease back in 2013.
But Billy hasn’t allowed the health ailment to slow him down as he was knighted at Buckingham Palace for services to entertainment and charity last year.
The Glasgow-born star, who has been married to wife Pamela Stephenson since 1989, admitted the momentous moment was “nerve-racking” as he was trying hard not to fall over.
Discussing the big moment in an interview with Radio Times, he said: “It was a big bit nerve-racking. You don’t want to make an a**e of it.
“You think, ‘Oh God, don’t trip.’ Or worry you might make a rude noise.”
Billy was diagnosed with the progressive neurological condition in 2012, with symptoms including slow movement, stiff and inflexible muscles and involuntary shaking.
And recalling the big day, the 75-year-old admitted he struggled to bend the knee in front of Prince William due to his condition.
He continued: “Since I’ve got Parkinson’s, I’m a bit dodgy getting down on one knee – I don’t do it all that well.”
“And then I had to walk backwards to a certain point, but I managed it fine.”
The actor went on to joke: “I’m sure Prince William will think I’m a mentally ill person.
“I answered his questions in the most stupid fashion just through nerves.”
When Billy originally learned he had been given a knighthood in the Queen’s birthday honours list, he admitted he felt a little “embarrassed”.
Talking to the BBC last year, he said: ”I am a little embarrassed but deep within me, I’m very pleased to have it.
“I feel as if I should be called Lancelot or something. Sir Lancelot, that would be nice. Sir Billy doesn’t quite have the same ring.”
Last year, Billy admitted he mocks the symptoms of his Parkinson’s disease during his performances.
The iconic Scotsman revealed he approaches his condition with humour by playing Whole Lotta Shakin’ Goin whilst performing on stage.
In an ITV documentary titled Billy Connolly And Me: A Celebration celebrating his career, Billy said: “The doctor said to me ‘You realise this isn’t curable?’ and I thought ‘What a rotten thing to say to somebody’.
“I always thought he should have said ‘You realise we are yet to find a cure?’, to put a little light at the end of the tunnel. There’s a lot to be said for that.”
He added: “When I’m in front of people performing I don’t give it much attention, I perform in spite of it. That’s why I put on Whole Lotta Shakin’ Going On, just to do that (swearing) to it.”
The programme looked back at Billy’s’s incredible long career that has spanned over five decades, from starting off as a folk-singer to being one of the greatest stand-up comedians of all time whilst also appearing in many hit movies.
Billy Connolly’s full interview with Radio Times can be found in this week’s issue, out now.