 His third and youngest son, Eric Maclagan (1879–1951) married in 1913 and left two sons, Michael Maclagan (1914–2003), herald and historian; and Gerald Maclagan (d. 1942, killed in action), who had been working in Rhodesian Railways.His posterity is represented by the three surviving children of Michael Maclagan.Maclagan was the younger brother of Professor Sir Douglas Maclagan, MD, otherwise known as Andrew Douglas Maclagan (1812–1900) and Sir Douglas, also educated at the Royal High School in Edinburgh, was a fellow of the Royal College of Surgeons of Edinburgh, 1833 and was knighted in 1886.