He's only 55, but George Clooney is already apprehensive about his 60th birthday.
ET caught up with the actor and his pal, Julia Roberts, at the Cannes Film Festival -- where they're promoting their film Money Monster, out May 13 -- and the Hail, Caesar! star candidly admitted that his next milestone birthday is the first one to really worry him.
Asked how he celebrated his big day on May 6, Clooney joked, "By mostly hiding in my room and crying because the next one is 60."
Leave it to a friend like Roberts to help you realize that age is nothing but a number, especially when you're George Clooney.
The five-time co-stars also talked about their recent epic session on "Carpool Karaoke," explaining that their decision to appear in the segment with a big-time singer like Gwen Stefani stemmed mostly from their lack of confidence in their own vocal cords.
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EXCLUSIVE: George Clooney dreads turning 60, celebrated 55 by 'hiding in my room and crying'
BEVERLY HILLS, CA - NOVEMBER 09: Actress Julia Roberts (L) and actor George Clooney attend the 2013 BAFTA LA Jaguar Britannia Awards presented by BBC America at The Beverly Hilton Hotel on November 9, 2013 in Beverly Hills, California. (Photo by Christopher Polk/BAFTA LA/Getty Images for BAFTA LA)
Sunday Calendar cover shoot of ' Oceans 11 ' cast members taken in Malibu, CA on 10/20/01. Cast members are Don Cheadle (front left) George Clooney, Julia Roberts, Brad Pitt, Matt Damon, and Andy Garcia. PHOTO BY ^^^/LA TIMES. NO SALES. (Photo by Anacleto Rapping/Los Angeles Times via Getty Images)
NEW YORK CITY - MARCH 4: Actor Benjamin Bratt, actress Julia Roberts and actor George Clooney attend the American Museum of the Moving Image Salutes Julia Roberts on March 4, 2001 at the Waldorf-Astoria Hotel in New York City. (Photo by Ron Galella/WireImage)
Julia Roberts & George Clooney (Photo by Jeff Kravitz/FilmMagic)
SANTA MONICA, CA - JANUARY 09: Actress Julia Roberts (L) presents actor George Clooney the Freedom Award onstage during the 11th Annual Critics' Choice Awards held at the Santa Monica Civic Auditorium on January 9, 2006 in Santa Monica, California. (Photo by Kevin Winter/Getty Images)
BEVERLY, CA - OCTOBER 13: Presenter/actress Julia Roberts (L) and actor/Director George Clooney pose in the press room at the 21st Annual American Cinematheque Award Honoring George Clooney held at the Beverly Hilton Hotel on October 13, 2006 in Beverly Hills, California. (Photo by Kevin Winter/Getty Images)
NEW YORK - MAY 05: (L-R) Actor George Clooney and actress Julia Roberts arrive at the Metropolitan Museum of Art Costume Institute Gala, Superheroes: Fashion and Fantasy, held at the Metropolitan Museum of Art on May 5, 2008 in New York City. (Photo by Stephen Lovekin/Getty Images)
BEVERLY HILLS, CA - NOVEMBER 09: Actors Julia Roberts (L) and George Clooney attend the 2013 BAFTA LA Jaguar Britannia Awards presented by BBC America at The Beverly Hilton Hotel on November 9, 2013 in Beverly Hills, California. (Photo by Kevork Djansezian/BAFTA LA/Getty Images for BAFTA LA)
BEVERLY HILLS, CA - NOVEMBER 09: Honoree George Clooney (R), recipient of the Stanley Kubrick Britannia Award for Excellence in Film and actress Julia Roberts walk off stage during the 2013 BAFTA LA Jaguar Britannia Awards presented by BBC America at The Beverly Hilton Hotel on November 9, 2013 in Beverly Hills, California. (Photo by Christopher Polk/BAFTA LA/Getty Images for BAFTA LA)
NEW YORK, NY - APRIL 19: Julia Roberts, George Clooney chat during a break filming Jodie Foster's; 'Money Monster' on April 19, 2015 in New York City. (Photo by Steve Sands/GC Images)
LOS ANGELES - APRIL 13: George Clooney, Gwen Stefani and Julia Roberts join James Corden for Carpool Karaoke on 'The Late Late Show with James Corden,' Wednesday, May 4th, 2016 (12:37-1:37 AM, ET/PT) on The CBS Television Network. (Photo by Darren Michaels//CBS via Getty Images)
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"They asked us to do one, just to sing, and I said, 'Why don't we sing with somebody else because we shouldn't be singing,'" Clooney revealed of how the Late Late Show With James Corden appearance came about. "We have heard each other sing and we should not be singing."