Naked photos of Justin Bieber have emerged online.

The teen pop star stripped naked to serenade one of his biggest fans - his grandmother.

Pictures obtained by celebrity site TMZ.com show the 19-year-old singer nude with only a carefully placed guitar to cover his manhood.

According to TMZ, the Baby hitmaker was spending Thanksgiving with his family at his grandmother's home in Toronto last year. During family games he made his grand entrance with an impromptu serenade - without clothes.

He sang: "I love you, grandmaaaa ... how are youuuu ... helloooo grandma."

His grandmother told him to get back to his room and get dressed, the site claimed.

His stunt made a change for his wayward behaviour of recent months.

Wayne Rennalls, a Long Island nightclub patron, is planning to sue him over a bar brawl.

Rennalls alleged that he was left bloody and bruised in the club car park after the heated exchange involving the pop superstar and his entourage which was sparked by "jealousy" over women.