Nicole Kidman says the key to her successful 18-year marriage to Keith Urban is in their bathroom — more specifically, their shower.

The 57-year-old actress admitted that she sings in the shower and, no surprise, so does her country music star husband.

"I also hear Keith singing in the shower, and I’ll hear his new songs forming," Kidman told W Magazine.

"We have a double shower. The double-headed shower: key to a successful marriage. Separate commodes and a double-headed shower!"

'THE PERFECT COUPLE' STAR NICOLE KIDMAN LIVES 'NORMAL LIFE' IN TENNESSEE WHILE DOMINATING HOLLYWOOD

Nicole Kidman and Keith Urban on Oscars red carpet split

Nicole Kidman shared the key to her successful marriage to Keith Urban. (Getty Images)

The Hollywood actress previously shared another key factor in their relationship. 

Keith Urban dons a tuxedo while Nicole Kidman wears whimsical pink Chanel gown to Met Gala

Kidman and Urban decided from the beginning of their relationship that they would only communicate by voice. (Getty Images)

NICOLE KIDMAN'S TENNESSEE HOME ALLOWS HER TO BE 'JUST A CITIZEN': 'MY KIDS LOVE THAT'

The couple decided from the beginning that they would only communicate by voice, Kidman told Parade magazine.

"We don't text," Kidman said at the time. "We call. We've done this since the very beginning. The reason it started at the beginning was because I didn’t know how to text, and it just kind of worked for us. So, now we don’t."

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"We just do voice to voice or skin to skin, as we always say. We talk all the time, and we FaceTime, but we just don’t text because I feel like texting can be misrepresentative at times," she added.

Keith Urban and Nicole Kidman at the US Open

Besides their no-texting rule, their secret to a lasting marriage is easy: "Not having secrets," Kidman said. (Mike Stobe)

Besides their no-texting rule, their secret to a lasting marriage is easy: "Not having secrets," Kidman continued.

In 2023, the country music star told Fox News Digital another way they keep their marriage strong.

"It’s always family first," Urban explained ahead of the ACM Awards. 

"It's balanced, so it means it goes out of balance sometimes, and we just put it back in balance," he said. "It's never perfectly in balance, but we get it back on track."

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Keith Urban nuzzles up to wife Nicole Kidman

Kidman and Urban rely on "skin to skin" or voice calls only in their relationship. (Angela Weiss)

Kidman and Urban share two daughters: Sunday Rose and Faith Margaret.

The "Big Little Lies" actress additionally has two adopted children with Tom Cruise: Connor and Isabella. 

Kidman has a reportedly strained relationship with those children, in part because of their participation in Scientology, alongside Cruise.

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Kidman and Cruise met while working on the 1989 film "Days of Thunder" and married in 1990. They adopted Isabella in 1992 and Connor in 1995. During their divorce in 2001, they shared joint custody.