Paul Rudd had to try not to "embarrass" himself with Michael Douglas.
The 49-year-old actor was a huge fan of the 'Wall Street' star so was delighted when they were cast together in 'Ant-Man' because he thinks the 73-year-old screen legend is "the greatest".
He said: "I didn't know him until we worked together on these films and I've been a fan of his my whole life so it was just admiration.
"I've had the good fortune of working with some real legends and there's the initial period where I just want to be cool, you know, and try not to embarrass myself and be respectful, but then also not fawn, and I think by day two with Michael, I was already all in. That guy is the greatest."
Paul - who has Jack, 12, and eight-year-old Darby with wife Julie Yaeger - is now proud to be able to call Michael a "friend" and admitted he's an even bigger fan of his now they've worked together.
He told heat magazine: "As much as I love him as an actor, and I love a lot of the films he's done, I have become an even bigger fan of the man.
"Our relationship has grown to the point where I feel like we're friends. We talk about our families and sports and current events.
2It's always great when he's on set because he's fun to hang out with.
"I would ask him stories about movies he's worked on and the people he knows, stories about his dad (Kirk Douglas) and he's very forthcoming - it's amazing.
"Getting to work with people like that is one of the coolest things."
And their closeness was very helpful when it came to working on new sequel 'Ant-Man and The Wasp'.
Paul said: "I felt like we just knew each other more and we know our characters.
"And he can also just make jokes at my expense and I love it. He's really playful. He's a blast.
"IT did, I think, make it easier, because we just knew each other better."