EXCLUSIVE: Justin Bieber Reveals the Key to 'Being Sexy' While Only Wearing His Underwear

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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."

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.