When you're on Ragnorok, first visit (I think) with Laguna and co on board, you can talk to them on another deck and hear along the lines of....

Kiros: You know Squall, you look a lot like your mother.
Ward: ....
Kiros: Ward says it's a good thing you don't look like your father!

I'd say that pretty much proves it
I was really surprised at the complete lack of reaction from Squall though.