prouder or more proud?

[yamyam]

Hello, teachers.

I've found the following sentence in a grammer exercise book.

1. He was all the more proud because he was the only person who got an A on the test.

According to several dictionaries, the comparative form of "proud" seems to be "prouder."
I think dictionaries are correct. If so, #1 is wrong? :-|

Thank you very much in advance for your help on this.

yam

 

[Rover_KE]

Both 'more proud' and 'prouder' are correct in this context.

The word 'proud' is preferred because it is preceded by 'all the more', but 'all the prouder' would be OK, too.