EXCLUSIVE: Justin Bieber reveals the key to 'being sexy' while only wearing his underwear

Kendall Jenner Joins Justin Bieber in Calvin Klein Campaign

Calvin Klein is continuing its partnership with Justin Bieber with new provocative ads, but this time the Biebs is bringing some friends along.

Kendall Jenner, Kendrick Lamar and other celebs are jumping in for the new spring global ad campaign.

WATCH: Justin Bieber Strips Down as the New Face (and Body) of Calvin Klein

"Being sexy is just being 100 percent comfortable with yourself," Bieber said in a behind-the-scenes clip from his shirtless photo shoot. "I am fearless by taking things one step at a time, and not focusing on the hardships but focusing on the success."

See Bieber through the years:

The Evolution of Justin Bieber
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EXCLUSIVE: Justin Bieber reveals the key to 'being sexy' while only wearing his underwear
Canadian pop megastar Justin Bieber (C) plays basketball with a young survivor of Super Typhoon Haiyan in Palo, Leyte province on December 10, 2013. Pop megastar Justin Bieber sang to and played basketball with young survivors of the Philippines' deadliest typhoon on December 10 after he flew into the disaster zone to boost an international relief effort. AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
LOS ANGELES, CA - JULY 27: The winner of Champ of Charity singer Justin Bieber (L) and singer Cody Simpson onstage at the 2014 Young Hollywood Awards brought to you by Samsung Galaxy at The Wiltern on July 27, 2014 in Los Angeles, California. The Young Hollywood Awards will air on Monday, July 28 8/7c on The CW. (Photo by Frederick M. Brown/Getty Images for Variety)
The "Baby" singer headed straight to the salon for a new makeover ... this time going blonde! (Instagram)
LOS ANGELES, CA - AUGUST 23: Justin Bieber attends a VMA Pre-Party hosted by Chris Brown & Pia Mia featuring Bera on August 23, 2014 in Los Angeles, California. (Photo by Araya Diaz/Getty Images)
NEW YORK, NY - JAN 17: General view of a Justin Bieber for Calvin Klein Billboard located on Houston Street on January 17, 2015 in New York City. (Photo by Tomas/IMAGES/Getty Images)
LAS VEGAS, NV - MARCH 15: Singer Justin Bieber arrives at Omnia Nightclub at Caesars Palace to celebrate his birthday on the nightclub's opening weekend on March 15, 2015 in Las Vegas, Nevada. (Photo by Gabe Ginsberg/Getty Images)
CANNES, FRANCE - NOVEMBER 07: Singer Justin Bieber attends the 17th NRJ Music Awards ceremony at Palais des Festivals on November 7, 2015 in Cannes, France. (Photo by Marc Piasecki/WireImage)
LOS ANGELES, CA - JANUARY 18: Justin Bieber and Corey Gamble are seen in Beverly Hills, Ca on January 18, 2016 in Los Angeles, California. (Photo by Light Brigade/Bauer-Griffin/GC Images)

This is Bieber's second time around with the label after his first outing with them last January. This marks round two for Jenner as well, who revealed that she wears the designer's clothes whether the camera is on her or not.

"The underwear is sick and amazing, and honestly I wear it every night to sleep," she said.

WATCH: Kendall Jenner Joins Calvin Klein's Sexy Spring Campaign

The new campaign had celebs fill in the blank for this sentence, "I _________ in #mycalvins."

Bieber wrote "flaunt," while Kendall wrote "be with you."

Lamar filled in his blank with the word "reflect" and he reminisced about his hometown roots behind the scenes, saying, "Compton means strength. You got to be a strong person to grow up in the inner city."

WATCH: Kendall & Kylie Jenner's Secret Boob-Slapping Handshake

Watch the video to see Bieber strip down to his boxers for the new ads.

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