Kirsten Dunst Says 7-Month-Old Son James Weighs 22 Lbs.: 'We Call Him Big Kahuna'

Kirsten Dunst has one big baby on her hands.

The 39-year-old actress made an appearance on Jimmy Kimmel Live! Tuesday where she gave fans a rare update on her growing baby boy, James Robert, whom she says is already almost as big as her 3-year-old son, Ennis.

"We call him Big Kahuna," Dunst told host Jimmy Kimmel with a laugh. "He's like 22 pounds for a 7 month old?! My wrist is killing me!"

"All he wants to do is bounce, walk, be like his brother and walk around," she added. "He just wants to walk and run, he doesn't even know what crawling is."

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The Spider-Man actress added that she's been sleep training James and was nearly sleep-deprived from the night before.

"I've been sleep training a 7-month-old so I had a crying baby all night last night so I'm hanging on by a thread," she told Kimmel with a laugh. "He was so good and then last night it was like the s--- hit the fan. I was sleeping a half hour in between shoving a pacifier in his mouth."

Dunst shares her two sons with fiancé Jesse Plemons. In September 2020, Dunst and Plemons told The New York Times about their relationship, which began in 2016 when they met on the set of Fargo.

"​​We became friends and first creative partners and for me that was the beginning of us getting together," the Bring It On star told PEOPLE about working together. "We want to do this over the course of our careers."

As their romance blossomed, Plemons and Dunst got engaged in January 2017. A year and half later, the Spider-Man actress gave birth to their first child together.

In August 2019, Plemons praised Dunst in a heartfelt speech during the actress' Hollywood Walk of Fame ceremony, which they brought Ennis to for his first official public event at the time.

"Aside from the brilliant actor you are, I've also had the even greater pleasure of getting to know you as a person outside of work," said Plemons at the time. "Seeing the kind of mother, wife, daughter, sister, friend and cohort you are is why I and all of your friends and everyone else are here today and why we all love you. It's for the incredibly generous and amazing person that you are."

Despite having a lengthy engagement, Dunst told Kimmel that they'll tie the knot "very soon."

"I just kept getting pregnant and I kind of want to enjoy my wedding," she joked during the show. "I just want to be able to drink and have fun."