Keleustanor is the son of Herakles and Iphis who was one of the daughters of King Thespius. During his stay in the court of King Thespius, Herakles impregnated 49 out of the 50 daughters of Thespius including Iphis who he lay with one night. The result of that particular encounter was Keleustanor.
"by Iphis he [Herakles] had Keleustanor"
- Apollod. Biblioteca 2.7.8