Talk about a royal hottie.

Photos of princess-to-be Kate Middleton in a bikini have hit the Internet -- and suddenly, everyone knows exactly why Prince William popped the question.

True, the photos were taken back in 2006, when she was vacationing with William in Ibiza, Spain. So while we can't be sure that Middleton still has the same washboard abs she once did, we do know the 29-year-old is still long, lean and lovely.

SODAHEAD SLIDESHOW: See the hottest royal hotties of all time.

After getting a look at a set of Kate Middleton bikini photos, it's a wonder Prince William took this long to settle down.

Middleton has plenty of competition, however: Blue-bloods, including her late mother-in-law, have been known to get pulses racing. From Middleton to Princess Diana to Queen Rania to Grace Kelly (not to mention a couple of sexy princes), let us know: Who is the hottest royal hottie?