To get back to the original debate, “proud” is one syllable. Thus, “prouder” is the correct form. This single-syllable adjective often seems to have more confusion than others, but technically, “prouder” is correct.

Is there a word like prouder?

Prouder and more proud are both correct and acceptable to use.

How do you use prouder in a sentence?

Each day he was prouder and fonder of the boy. Neither man nor army could have a prouder memorial. That was fine of you and makes me all the prouder to have your friendship. She was prouder of his friendship than of anything that had yet come to her.