Jennifer Aniston says she had a hard time getting to grips with the premise of her new film The Switch.

The friends actress stars as a 40-year-old single woman who opts for sperm donation to become pregnant. However, seven years later, she finds out her best friend Wally (Jason Bateman) replaced her preferred sperm sample with his own.

"I've never laughed harder. We actually had a hard time rapping our heads around, like, how could this possibly happen? It's so insane," Jennifer said.

"That's why we loved it. It's such a unique story. It's sort of the modern family," she added.

Jennifer, 41, also spoke very highly about her co-star and old friend Jason Bateman:

"He's sweet as can be and he's fun and a commited actor. I've know Jason for a long time and he's been down some roads and he's just better than ever."

The Switch is out in cinemas now.