The 45-year-old star won Best Actress at the 2019 Academy Awards for her role in 'The Favourite' and although it was a high point of her career, she has very little memory of the evening because she was in the bar getting "bladdered" for most of it.
She said: "I actually can't remember it. The great thing about the Oscars is there is a bar just behind (the auditorium) so everyone is there. There are hundreds of seat fillers so almost everybody is in the bar getting bladdered!"
The 'Broadchurch' actress is returning to the small screen as Queen Elizabeth in series three of 'The Crown' and though she did little to prepare for the regal role, producers had to enlist a movement coach to teach her to walk more gracefully.
Appearing on 'The Graham Norton Show' alongside her co-star Helena Bonham-Carter, she said: "I did nothing, though I did have a movement coach, but still I walked like me, or rather like a farmer!"
Helena said: "I do everything to prepare and Olivia does nothing, and she ends up being completely brilliant."
The two actresses had a great time working on the Netflix drama.
Helena said: "It really is fun. We've been together for so long, but we still like each other."
After landing her role as the queen, Olivia met Prince William and though he was "very charming and lovely", the actress was disappointed to learn he doesn't watch the show, which is based on the life of his grandparents, Queen Elizabeth and Prince Philip.
Asked if she'd met any royals since getting the role, she said: "Yes, but it didn't go very well. I met Prince William at a dinner and he asked what I was doing at the moment before he quickly added, 'Actually, I know what you're doing'.
"I was so excited and asked, 'Have you watched it?' His answer was a firm, 'No.' But he was very charming and very lovely."
The full interview airs on 'The Graham Norton Show' on BBC1 on Friday (08.11.19) night.