Hugh Bonneville recalls being "absolutely terrified" doing his first scene with Dame Maggie Smith on Downton Abbey.
The actor, 52, who played Lord Grantham, said he is already beginning to feel "nostalgic" after the hit drama ended with an eagerly anticipated finale in December.
Bonneville said working alongside Dame Maggie, who played the Dowager Countess, made him raise his game.
Speaking on Desert Island Discs, he said: "I can remember the very first scene I did with her and I was absolutely terrified, and I think I can remember the last scene with her and I was absolutely terrified.
"She is the most astonishing actress. Her wit is legendary, as you say, and she doesn't suffer fools. And you raise your game, you have to.
"It's great acting opposite her because she's got extremely high standards for herself and expects them of others."
He added: "I think I'm already sort of nostalgic about it. It was an extraordinary rollercoaster of a show, to be involved with something that you thought was going to last six or seven episodes, as we did in the first series, and then 52 episodes later we've said goodbye.
"And those people involved - I think there were about sort of 40 or 50 people who'd done every episode, been both in front of the camera and behind - and the hundreds of crew who'd come and gone over the six years.
"It does become a second family. So the final farewells were sad, but obviously the freedom ... normally, I'd be gearing up to don the thermals and start shooting again in Highclere Castle, so it's a strange feeling not to be doing that. But happiness tinged with fond memories."
Downton Abbey debuted on ITV in 2010 and became a global phenomenon, collecting numerous awards along the way.
It also grew into a pop-culture favourite with spoofs and parodies from Sesame Street and The Simpsons, to name a few, lighting up social media.
:: Desert Island Discs is broadcast on BBC Radio 4 at 11.15am on Sunday.