Wikipedia states
Astydameia, daughter of King Mygdon, who was killed by Heracles who sided with Lycus in a conflict opposing Lycus and Mygdon. After killing her father, Heracles sired a son named Berecynthus with Astydameia.
The source cited is William Smith. A Dictionary of Greek and Roman biography and mythology. s.v. Mygdon. London (1848), however, none of the Mygdons covered in that dictionary are said to have a daughter Astydameia or grandson Berecynthus by Heracles.
Is there any ancient source that made such a claim? Or was this fabricated whole cloth by a Wikipedia editor?
In ancient sources such as Pseudo-Apollodorus and Diodorus Siculus, Astydameia is the daughter of Ormenion or Amyntor and mother of Heracles' son Ctesippus. Pseudo-Apollodorus mentions Heracles killing Mygdon but makes no mention of siring a son with his daughter.
The only results I could find not parroting Wikipedia was that the Dactyls, one of which was named Heracles, discovered iron on Mount Berecynthus