Justin Bieber serenaded a couple on their honeymoon.

The 'Boyfriend' hitmaker was vacationing in Bora Bora in French Polynesia when he came across bride Katie Wollesen and her new husband and sang for them as they sat down to eat.

But the evening then took a more raucous turn as he joined them in a drinking game.

Posting a picture on Twitter of herself and a female pal, Katie wrote: ''Thank you @justinbieber for serenading us at dinner, challenging us in flip cup, and leading the winning team in the first annual coco bowl! #honeymooninwiththebiebs.(sic)''

Justin replied: ''not sure what face I'm making but.. Lol. Nice meeting u and happy honeymoon :) (sic)''

The 21-year-old singer also shared a photo of himself with the newlyweds and other pals on his Instagram, in which he was carried topless by the group.

He wrote: ''Met and hung out with the coolest married couples last night and then this happened (sic)''

Sharing the same photo on Twitter, he added: ''Congrats to my honeymoon crew. Good people (sic)''

Justin caused a stir on his vacation earlier this week when he shared a nude photo of himself looking out to sea, with his butt on display for the camera.

The picture was mocked by his friend Miley Cyrus, who altered the image to give him a larger derriere, and also compared his rear to Rihanna's.