Justin Bieber: I'm not gay!

Justin Bieber has clarified that he's not gay on Instagram.

The 21-year-old took to the social networking site on Sunday to post a video in which can be seen skateboarding on a plane before planting a kiss on a male friend's cheek.

He's used to putting up with speculation online but this time he didn't give anyone a chance.

"@mikeyarana I'm not gay but even if I was that's not an insult (sic)," he posted.

It seems the young star has been feeling philosophical lately, as he's shared some of his deepest thoughts on the internet. He took to Twitter last week to give some advice to people who feel let down or upset.

"People will try to take advantage of u...they will try to tear u down. Keep your head up and know your truth. Be kind in the face of anger (sic)," he wisely wrote.

Justin has turned over a new leaf after facing trouble with the law last year. He has publically apologised and is upset he let things get so far.

"I was rebelling a little bit. I was getting cockier and cockier. I didn't have people to check me," he told Seventeen magazine recently. "I looked back and I was disappointed in myself. You have to own up to the mistakes. You have to say, 'I'm sorry if I've let you down.'

"I always want to be honest and let people know that those mistakes aren't who I am. Who I am is someone who really cares about people. I need healthy relationships with people I can feel safe with. People I can say whatever to, and I'm not going to be judged."