I know the father is his highness but.. this is a flashback right?

Yes.

Thank you (づ￣ ³￣)づ

So that's why one of the guy here said that he saw louise with a man before and the color of his hair was red.

That's correct - this flashback is answear for Maetels closet full of wigs. Now we know for sure, how it was that night, when bby got pregnant.