Helio Castroneves Has IMPORTANT Dancing Advice for Prince William

Prince William needs help ... 'cause his dancing sucks ... and Indy legend Helio Castroneves (who also won "Dancing with the Stars") is offering up his expertise!

Helio joined the guy on the "TMZ Sports" TV show (airs tonight on FS1) ... and channels his inner-Bruno to help out the future King of England.

Watch. Listen. Take his advice!!!