Albert married Catherine Robson in Cambridge in 1940. They had two children: Naomi, born in 1944 and a son, William Neil, known as Neil. Naomi was killed in a car crash in the USA in 1966.
Catherine died of cancer 14 November 1963. Two years later, on 10 December 1965 Alexander married Gisela Gudrum Baker (née Zutavern, of Heidelberg), the widow of Kingsley Ferguson Baker, a Sydney industrial chemist, at the Presbyterian Church in Pymble. Stricken by a brain tumour in 1969 when serving as dean of science, he died at his Mosman home on 23 May 1970 and was cremated. His wife, and the son of his first marriage, survived him. The Pymble Church “was packed by friends, colleagues, and students on 26 May for a funeral service during which a moving panegyric was spoken by Professor I.G. Ross”.
One obituary summed up Alexander the man thus: