Tina Fey and Amy Poehler's friendship is "like a marriage".
The former 'Saturday Night Live' co-stars are starring in new movie 'Sisters' together and revealed their history is very important to them both.
Amy said: "It's like a good marriage. My mom always says it's very important to have people in your life who knew you when. The older you get, the more you treasure that idea of someone knowing your family and where you came from, and being around during these times and these times. Tina and I, we don't have any sisters."
However, Tina joked that the secret to their friendship is that "we don't see each other very often".
Meanwhile, the pair revealed they love working together because it means they don't have to deal with any potential awkwardness with new people on set.
Amy told US Glamour magazine: "There's usually this moment at the beginning of a film when you have to go out for dinner and talk to the person and be like, 'How do you like to work?'
"We didn't have to do any of that when we first started 'Sisters'."