Time Crash: Children in Need Special

Summary:
Martha leaves the Doctor and the Doctor wants to travel somewhere on his own. Suddenly the Tardis goes crazy and he faces his fifth incarnation. He knows exactly who is in front of him but the Fifth Doctor doesn't and he thinks that Ten is a fan who somehow got onto his Tardis. While Five tries to solve the problem of two Tardises in one place the Cloister bell rings. Then Ten whirls around the console and he manages to separate the two time stream because he has watched himself doing it before. Now the Fifth Doctor accepts that he's facing his future self and warns Ten to not forget to put up his shield again.

This episode is just brilliant when the two incarnations of the Doctor meet and one knows exactly who the other is but the other one doesn't. I really like the part when Five thinks that Ten is a fan and that he somehow sneaked into the Tardis to be close to his idol. Another great part is, that there would be a hole in the fabric of time of the exact size of Belgium when they can't solve the problem with the colliding timelines. That always makes me giggle. You don't need to watch the episode to know what happens in the Doctor Who universe but it's a great extra and very funny.