Leah chats to Sarah Jane actress Elisabeth Sladen
David Tennant is starring in the Sarah Jane Adventures, in a special two-part story on Thursday and Friday.
The actor plays Doctor Who in the episodes, and has to save the day when disaster strikes Sarah Jane's wedding.
Sarah Jane, played by Elisabeth Sladen, was the Doctor's assistant in the series back in the 1970s, and made an appearance alongside David in 2006.
David is being replaced as Doctor Who by actor Matt Smith who will appear as the 11th Doctor next year.
David's next outing as Doctor Who will be in an episode called The Waters of Mars in November and his last appearance will be in a big two-part story over Christmas.
You can watch David on the Sarah Jane Adventures on Thursday and Friday at 4.35pm on CBBC on BBC One.