Felipe wasn’t an ugly guy he was a tall and handsome young man at that time, with the fact that Letizia fell to her first husband who was her teacher (not Crown Prince) or her other ex (the anchor guy if the rumour is true); and both weren’t even close to Felipe in looking department, then I wouldn’t be surprise if Letizia still fell in love with Felipe even without his HRH title.
Exactly, especially when she meets up her M 'sisters' and their hubbies, she probably can't believe how lucky she is (OK excluding MM).