Nikolai Sorin

Count Nikolai Sorin (PROSE: Happy Endings) was the great-grandfather of Sorin. Ace, who had met his great-grandson in 1943, (PROSE: The Curse of Fenric) came to live with him for a time. (PROSE: Set Piece, At Childhood's End) She would tell Bernice Summerfield that he was the 63rd person whom she had sex with. (PROSE: Happy Endings)

By one account, Ace, whilst still traveling with the Seventh Doctor, was shown a number of possible futures in her timeline by a Quantum Anvil, which included living with Sorin's ancestor. This incident led her to leave the Doctor. (PROSE: At Childhood End)