Reese Witherspoon refuses to call Laura Dern by her first name to avoid confusion with her own real moniker.

The 'Legally Blonde' actress has admitted she has to call her 'Big Little Lies' co-star by her surname, although their castmate Nicole Kidman thinks it "sounds so weird".

Speaking to Vanity Fair, Nicole said: "I hate how you call her Dern. It sounds so weird.

"I'm always like 'Laura,' and you're like 'No, Dern, Dern,' and I'm like, 'Why?'"

Reese quickly interjected: "'Cause my name is Laura, and her name's Laura, and it's confusing to me. My real name's Laura Jeanne.

"So, I get confused so I just call her Dern. Because we can't both be Laura."

Nicole, 56, forgot her castmates share the same first name, but she was still confused by the whole situation.

She pointed out: "She doesn't even call you Laura, though."

Reese, 48, quipped: "You're trying to understand something that just makes no sense."

Her full name is actually Laura Jeanne Reese Witherspoon, and she took on her mother's maiden name when she started acting in the 1990s.

Fans were shocked by the revelation, with plenty of people replying on Instagram to voice their amazement.

One fan replied: "Reese Witherspoon’s real name is Laura Jeanne and I feel LIED to."

Another follower joked: "I was today years old when I found out Reese’s real name is Laura lmao."

And a third person laughed: "Today I learned Reese Witherspoon is Laura Jean. What is LIFE? (sic)"

Reese first got her start in showbusiness aged seven with a role in a florist's commercial, and by aged 14 she was making her feature film debut in 1999 movie 'The Man on the Moon'.

Back in 2021, she reflected on the part and wrote on Instagram: "I had no idea the journey that lay ahead of me. But I am so deeply grateful for all the ups and the downs that brought me to this moment."