In Robot of Sherwood, the Doctor mentions to Robin Hood that he's met Richard the Lionheart. This is a reference to his Crusade serial during his First incarnation. In it, he becomes involved with King Richard trying to marry off his sister, Joanna, to the Saracen ruler called Saladin. Joanna is not having it, and Richard believes that the Doctor is interfering with his plans. The Twelfth Doctor tells Robin Hood that he learned sword-fighting from King Richard, but that is never shown during The Crusade storyline. Either the Doctor is exaggerating, as he often does, or it happened off-screen. From what fans have seen of his earlier selves, the Doctor didn't really begin to hone his fighting skills until his Third self.