He still didn't know he's the father of baby??

He still doesn't know he's pregnant

So what is he thinking now telling him I'm pregnant after sex with him as a excuse of this.

From the spoilers I've read, he doesn't tell because he doesn't remember who he slept with. He's just guessing about the father having red hair. The Prince basically finds out by accident but doesn't know right away that he's the father

Fecccck