Casimir, the sixth but fourth surviving son of the Ducal couple, was born in 1138, shortly before his father's death, but also is possible that he born shortly after, and in consequence, was posthumous.
Casimir, the sixth but fourth surviving son of Bolesław III Wrymouth, Duke of Poland, by his second wife Salomea, daughter of Count Henry of Berg, was born in 1138, probablyly on the brink of his father's death. It is however also possible that he was born shortly after, and in consequence was posthumous.