Kristen Bell's daughters think she's twice her age.

Kristen Bell

Kristen Bell

The 'Good Place' actress turned 39 on Thursday (18.07.19), and just before she celebrated her birthday, she asked her two daughters - Lincoln, six, and Delta, four, whom she has with husband Dax Shepard - how old they think she is, and received some surprising answers.

In an Instagram video, Kristen asks her girls - who are kept off camera - how old they think she's turning, and youngest daughter Delta answers first, as she says: "Six ... 50 ... 63."

And after trying to hide her shocked expression, she then asks Lincoln the same question, who comes up with an even more outrageous figure.

Kristen asks: "How old do you think I'm turning, Link?"

To which the eldest child replies: "89."

The 'Frozen' actress then hopes her husband can give her a more accurate answer.

She asks him: "Okay, Dad, how old do you think I'm turning?"

But Dax says: "I think a safe bet, somewhere in the middle of those two guesses, so ... 71?"

At the end of the video, Kristen then reveals she's actually at least 24 years younger than any of their guesses.

She captioned the sweet video: "My kids are kind. I dont care if they cant do math (For my #armcherries : #fastmath is overrated.) (sic)"

Meanwhile, Kristen previously praised her daughter Delta for being "social", as she'll strike up a conversation with just about anyone.

She said: "It boggles my mind how social [Delta] is. When we're on an airplane, she spends the majority of her time up in the front cabin either talking to the pilot or the stewardesses, not with me. She's four years old.

"I took her to the dentist the other day and I was trying to leave the dentist's office and I was like, 'Where is she?' She had walked into the dentist's office and was just talking to him. Just talking to him about things she had done that morning. Mind you, she just turned four, so she's a kid, you know?"