David Tennant, known to many as the 10th Doctor from Doctor Who, had to give David Letterman a bit of a lesson about the show when he appeared on Wednesday October 29th. He appeared to talk about the current show he is on called Gracepoint, which is the American remake of the UK's Broadchurch that he also stars in.
Tennant began talking about the show and threw in a great joke, "it's been running 50 years, almost as long as you have," to Letterman which produced many laughs. Letterman also asked if he's still on the show and Tennant told him Peter Capaldi is currently The Doctor and said he's 'fantastic'.
When Letterman asked about how many doctors there have been, Tennant began a complex description, "Capaldi is the 12th, but also there's another one so you could say there's been 13, and there was a movie version, so you could say there was 14. Approximately 12."
Check out the video of his apperance:
Tennant's doctor is one of the most beloved, and often ranked as the best, doctor incarnations from the show. His doctor regenerated into the 11th Doctor, played by Matt Smith, back in 2010 and he returned in 2013 to reprise his role for the 50th anniversary episode.