United Kingdom, June 4 -- Jennifer Aniston is so close to Friends co-star Lisa Kudrow that Lisa's son even used to call her "Mummy".

The 57-year-old actress spoke to Lisa as part of Variety's Actors on Actors series, where they reflected on their time on the beloved US sitcom - filmed on the same stage at the Warner Bros. lot as Lisa's new TV show The Comeback.

Lisa's son Julian also stars in the third series of the programme, with Jennifer saying of the filming location: "It's like he grew up hearing laughter all the time."

Lisa added: "I know. Can you imagine? Just the amount of joy. Because it was the most fun."

Jennifer then smiled: "He is today one of the most joyful human beings that I get to spend time with. Like, I love him. ...