Totally fiona_conn's fault.

[mrv3000]

Captain Jack is the Doctor's son.

Nonono. It makes sense. Some sort of rumor about the Doctor having a son that he might find. Jack appearing in the finale...

Face of Boe: The great secret is that you have a son.

Doctor: Wicked! Who'd I knock up?

Face of Boe: His name was Cameron.

Doctor: Ohhhhh. Right.

Face of Boe: Would you like to meet him?

Doctor: Already met him, thanks. He wasn't exactly...oh. You mean my son.

Face of Boe: Yes, you git.

Doctor: Hey. Sure. Why not. Not feeling awkward in the least right now. Let's do this thing.

[Jack appears from behind the Boe tank]

Jack: DADDY!

Doctor: Oh hell. Okay, someone's getting therapy for that kiss.