Alex Marcel van Westerborg was a son of Salomon van Westerborg (passed away 13 March 1932) and Antoinette Elizabeth Fles. He married 25 September 1941 in Rotterdam Bertha Galewski, a daughter of Mozes Galewski and Mirjan Freimann.
Alex was born into a family of three children, of whom he and his brother Abraham were killed in the Shoah. His eldest brother survived the Holocaust.
City Archive of Rotterdam, family registration card of Salomon van Westerborg.