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."
-Bang! showbiz