Ahiru no Oujisama
(aka Duck Prince
) is a manga by Ai Morinaga, first published in 2001. No anime exists for it, despite the fact the manga got picked for an English release. (By a yaoi line, too, even though this series is romance with no yaoi.)
Reiichi is a stereotypical nerd - he's short, wears glasses with spirals and...has a serious case of bowl hair. However, he desperately wants to get together with Yumiko, the prettiest girl in school. After being run over by a car and being disfigured beyond repair, he gets turned into a bishonen. Why? Reiichi was trying to save Yumiko's dog Mister when he was hit by that car, and Mister just happens to be a prince of a magical kingdom who had a tiny bit of magic left. What's worse, when he starts thinking perverted thoughts about Yumiko, he reverts to his old appearance!
Ahiru no Oujisama contains examples of: