Arsinoe of Macedon was a Macedonian noblewoman and the mother of Ptolemy, Pharaoh of Egypt. Arsinoe was of the Argead dynasty, and originally a concubine of Philip II, king of Macedon, and it is said she was given by Philip to Lagus, a Macedonian nobleman, while she was pregnant with Ptolemy I Soter I, but it is possible that this is a later myth fabricated to glorify the Ptolemaic Dynasty. Wikipedia