There are PLENTY of guys who collect Disney Princess stuff, and Disney stuff in general.

Uncommon, sure, but there's nothing wrong with it.

Why would it be strange ?

It's different, but that doesn't mean it's bad. I was always made fun of for being a girl that was into super heroes and other things aimed at boy. So I don't really see that boy liking princesses is any worse than me being a girl and liking super heroes

Speaking as a man, I never feel awkward buying merchandise unless someone is staring at me like I've grown a third head. I think it is perfectly normal for boys to be into Princess movies and their merchandise because these movies and characters are universal and do, in fact, appeal to all audiences, without gender restrictions.
I would not find it strange if my son asked me for a princess toy nor would I find it strange if my daughter asked me for superhero comics, because its what they like and what they want. The gender stereo-typing going on in this post is, quite frankly, a little insulting.

its ok and fine and normal

^^ nice to hear it from a guy's perspective!

We are allowed to like whatever we want.

Fun fact: Mulan is one of my brother's favourite movies. Yes, it's about a war, but the main character is a girl and considered to be a princess by Disney. He certainly doesn't seem to have anything against Mulan as the protagonist.

@MelStrachey said everything I was gonna say