If Justin Bieber were Kate Middleton's boyfriend, he'd make sure he had a full head of hair.
The Biebs slammed Middleton's husband, Prince William, for his thinning hair in a recent interview with the U.K.'s Rollercoaster magazine. He even offered some advice to His Royal Highness.
"I mean, there are things to prevent that nowadays, like Propecia," Bieber said of the hair-loss treatment.
"I don't know why he doesn't just get those things, those products. You just take Propecia and your hair grows back. Have you not got it over here?"
The Canadian-born singer, 18, who's dating actress Selena Gomez, has luscious famous locks himself. But while Bieber has the hair, Prince William has the girl.
The prince, 30, has been seen around London cheering on Great Britain during the Olympics alongside his smiling princess. Take that Bieber.