He assumed Bill was Molly and Arthur's boy. It did make him smile a little to think of having a son who was like a big brother to Harry's children. Even if that meant he'd had Teddy a bit late in life.
He blew out a thoughtful sigh before he shrugged his shoulders, unsure where to start.
"Ah ... well... Who is Teddy's mother? Were we married?" He decided that was a good place to start and left off the question about whether or not Teddy had been planned. Perhaps with the wolfsbane potion, he hadn't been as concerned about the danger he could pose to possible family members.