Herakles slept with fourty nine of the fifty daughters and had fifty-one children. Prokris bore two children (Antileon and Hippeus) and so did one of the other fourty-eight daughters. Unfortunately the record telling which of the daughters bore Kreon has been lost. Subseuently, other than Antileon and Hippeus it is impossible to determine which of Herales' children who were born to the daughters of Thespius is Kreon's twin. All that can truly be known is that other than Prokris and the daugher who went on to become a priestess, any of the women listed in the category The Daughers of Thespius could possibly be this unnamed daughter who is the mother of Kreon.
King Thespius & Queen Megamede (possibly one of Thespius' mistresses)
Spouse & Lovers
Herakles (lover for one night)
... he [Herakes] had Kreon - Apollod. Biblioteca 2.7.8