Christopher (The Unicorn and the Wasp)

Christopher was a name assumed by a Vespiform which came to Delhi on Earth to learn about Humanity. While undercover in human form he had a romantic encounter with Lady Clemency Eddison and impregnated her with a child, which while Vespiform, was still locked in human form, and knew nothing of his descent for most of his life. Christopher eventually drowned in the great monsoon of 1885. (DW: The Unicorn and the Wasp)

Torchwood had some knowledge of his presence in Delhi, though their understanding of the events was very limited and they were unaware of the existence of his son. (Captain Jack's Monster Files)