I got to tell you, I’m really surprised that Robert Hardy wasn’t actually ever in legitimate Doctor Who.

Change, my dear. And it seems not a moment too soon.
Look. I’m really sorry about this, but it’s late, and I’m tired, and I can’t manage a good cod-realistic sounding Big Finish-style back-of-the-CD blurb. Just look at the picture. It’s the fifth Doctor and an alternate sixth Doctor teaming up to fight the Doctor’s evil estranged son. And it’s clever because of real-world relationships between the actors and the characters they have played, and because back in the ’60s, Bill Hartnell had this crazy pitch where he’d be double-cast as The Doctor and the Doctor’s evil estranged son. That’s it. Enjoy.
Starring Robert Hardy and Peter Davison as The Doctor
Also starring David Tennant as Junior and Carole Ann Ford as Susan