Thin-on-top PRINCE WILLIAM gets Hair Clubbed by mop topped punk Justin Bieber after he took a cheap shot at Britain’s fab lad – for going bald!

The Biebs – who boasts a full head of lush locks – suggested in a recent interview with a British re­porter that the follically-challenged 30-year-old royal should start in­vesting in hair-growing products.

“I don’t know why he doesn’t just get those things, those products,” Bieber said. “You just take Pro­pecia and your hair grows back. Have you not got IT over here?”

While William’s hairline has no­ticeably receded over the past few years, his bald spot has also been growing – a genetic trait that he seems to have inherited from his father Prince Charles, who’s even joked about it.

“The thing about growing older is that your children get taller than you so they can see your bald spots,” Charles wise­cracked at the formal wedding breakfast after William married the former Kate Middleton in April 2011.

Thin-on-top William has also had to play second fiddle to his hirsute younger brother Prince Harry, who’s blessed with a thick shock of unruly red hair.

Meanwhile, the British press is up in arms over boorish Bieber’s slap at their beloved royal’s shrink­ing mane.

“While he’s brushing his golden locks, Bieber also needs to brush up on his manners,” sniffed one royal watcher.

“He should remember that he’s just a rock star. One day, William will be king – thinning hair and all!”