Rosamund Pike "wasn't sure" if Chris O'Dowd would accept his role in BBC Two short-form comedy series 'State of The Union'.
The 'Gone Girl' actress and the 'Bridesmaids' actor play estranged wife and husband Louise and Tom in the series - which is comprised of 10, 10-minute-long episodes - who get drunk before having their weekly marriage counselling session, as they fall back in love with one another despite an affair that caused them to break-up in the first place.
Rosamund didn't know whether the Emmy-nominated star would be interested in the role because she didn't think he would be impressed with her "comedy credentials", but she is "really delighted" he accepted the offer.
She said: "I was really delighted when Chris said he would do it.
"I wasn't sure whether he would take the role...I didn't know whether he would think that my comedy credentials were kind of up to the mark.
"I thought he might feel a bit superior but it turns out he didn't or he managed to put any feelings like that to the side."
The 40-year-old star says she was made up because she had been a huge fan of Chris' work for a long time, and admitted it felt like she was "putting [herself] on the line".
She said: "I have admired him hugely and I find him very, very funny.
"I hoped because I was already casted, you hope that someone is going to say, 'Yeah, I'm going to jump into this with her.'
"You never know though ... It's like putting yourself on the line in the dating game isn't it, but in a professional sense.
"So I was really pleased because you know I've done comedic stuff but it's not what I'm known for and this is obviously comedic and it's got a level of truth and humanity to it as well."
The pair bonded immediately and would practice their lines over a few glasses of wine.
She said: "Every night in the pub we'd finish work and Chris and I would sit outside in the garden of the pub that we working in and we'd have a glass of wine and go through the scripts for the next day.
"We'd come back and jump forward a week and do that.
"We never met ... we had said hello to each other for a short period of time."
'About A Boy' writer Nick Hornby has penned the script and 'Florence Foster Jenkins' director Stephen Frears has helmed the project.
'State of The Union' will be available on BBC Two and BBC iPlayer from September 8th.