Expertly coiffed pop star Justin Bieber doesn't understand why Prince William's hair is thinning.

And sure, maybe he's saying what we're all thinking, but his attack on the prince's encroaching baldness does seem a bit out of left field.

In an interview with U.K. magazine Rollercoaster, Bieber mused—

I mean, there are things to prevent that nowadays, like Propecia. 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?

Harsh words from a Canadian.

It's true, though: Propecia is readily available. And while it's expensive and not covered by most insurance companies — not that I'd know from personal experience — I'm pretty sure the royal family could take the hit.

Maybe Prince William just doesn't care, though. Apparently he and Prince Harry (who still has a full head of hair) joke about it. "But that doesn't mean a kid like Justin can come sauntering in and join in on the joke," says British journalist Jessica Callan.

Anyway, here's what Prince William (and a bunch of other celebrities) would look like with the Bieb's hairstyle. Also included: a bald Justin Bieber that can't be unseen.

[Image via AP]