Justin Bieber ''crossed the line'' when he sent a picture of himself in his underwear to Mark Wahlberg.

The 44-year-old actor has confessed he was shocked to receive a semi-nude photograph of the 21-year-old singer after he was unveiled as the face of Calvin Klein despite being good friends with the star.

Mark - who has also modelled for the underwear giant - said: ''He sent me a picture and I was like, 'Dude, don't send me a picture of you in your underwear. That's crossing the line. I don't need to see a picture of you in your underwear.''

The 'Ted' star added that while he accepts he might end up seeing Justin's Calvin Klein campaign, he is still going to try and avoid looking at his pal half-naked.

He told E! News: ''I'll probably see it when I'm driving down the street, and I'll still try to avoid it.''

The 'Boyfriend' hitmaker - who is currently on tour promoting the brand with model Kendall Jenner - previously came under fire for the ads, in which he starred with blonde beauty Lara Stone, after it was alleged his body had been photoshopped.

However, Justin laughed off speculation that the images were digitally enhanced to improve his physique by posting a photo of himself showing off his muscly body while wearing only a towel to cover his modesty on Instagram.

He captioned the image: ''Photoshop lol.''