I don’t know why people keep saying he doesn’t have sex with humans. At the very least he’s had sex with River Song, who while being timey wimey is still human and I believe they also have implied he’s “known” at least one Queen of England (in the Biblical sense).
I especially like the way he seemed the same sort of tag-along, make-do boyfriend that Mickey had been; and then, slowly, this deeper, better character and relationship emerged. And he does get bad-ass when he goes to war.
I don’t think this is worthy of spoiler tags, how did Sarah Jane get K-9, last I remember Sarah never met him, he was introduced with Leela, or am I mistaken. BTW Sweet reunion with SJS and Tennant.
In the first spinoff from Doctor Who, called “K-9 and Company,” Sarah Jane received a package from the Doctor, containing K-9. Apparently she kept him…
And Sarah consequently has K9 at the start of “The Five Doctors”.