Bieber lashes out in London   Play video Watch out for a Justin Bieber breakdown

Justin Bieber’s grandparents are reportedly "shocked and ¬terribly saddened" by the pop star's headline-grabbing antics during his trip to Britain and fear he is partying too hard because he has been led "astray" by a bad crowd.

The Baby hitmaker has been beset by problems during the U.K. leg of his Believe tour, which he wrapped up in London on Friday night. His woes included a birthday bust-up with bouncers at a nightclub and a furious altercation with a photographer hours before his final gig at London's O2 Arena.

Bieber also infuriated many fans by leaving them waiting for hours at his first show at the venue in London on Monday, and sparked concerns for his health when he collapsed backstage during Thursday's concert.

His grandparents, George and Kathy Bieber, have now admitted they feel "shocked and -terribly saddened" after hearing of the singer's exploits, and insist the 19-year-old needs to curb his partying, according to Britain's Sunday Express newspaper.

Kathy, 56, says, "I don't think for one moment this is all about him being a bad boy. He's only just turned 19 and he's still learning to cope with the pressures of fame. But it's worrying. You read all sorts of things about him partying and he needs to ¬understand some of those so-called friends probably don't have his best interests at heart... Justin is a sweetheart. He just needs to be kept away from unsavoury people who want to bask in his limelight and lead him astray."

Kathy also hopes her grandson will go back to London soon and put on a free show for all the fans who had to leave before he finally took to the stage for his much-delayed Monday night show at the O2 Arena: "I know he will be feeling ¬depressed about the way things have gone in London, so maybe it would be a good idea if he were to go back there later and perform free for the fans who feel let down by him. He's a boy with a wonderful heart who will want to make amends."

Bieber's grandfather George also reveals the star's mother, Pattie Mallette, will be having a heart-to-heart talk with her son over his behaviour, adding, "Pattie is ¬going to have a lot to say when she eventually sits him down for a quiet chat. And she will make sure he gets back on track, even if she has to put her foot down."