Patroklus is the son of Herakles and Pyrippehe who is one of the daughters of King Thespius. During his stay in the court of King Thspius Herakles impregnated 49 of 50 Thespius' daughters including Pyrippehe who he lay with one night. The result of that particular encounter was Patroklus.
Parents
Ancient Text
"by Pyrippehe he [Herakles] had Patroklus"
-Apollodorus.Biblioteca, 2.7.8