Ptolemy Keraunos
In 281 BC, Lysimachus died in battle and Arsinoë fled to Cassandreia (). There, she married her paternal half-brother Ptolemy Keraunos. Ptolemy Keraunos was a son of Ptolemy I Soter and his first wife, Eurydice of Egypt. The marriage was for political reasons: both claimed the throne of Macedonia and Thrace (by the time of his death Lysimachus was ruler of both regions, and his power extended to southern Greece and Anatolia). Their relationship was never good.