Dermot McGillycuddy (1911-1974), of Bishopscourt, Straffan, Co. Kildare was the second son of Senator, Lieutenant Colonel The McGillycuddy of The Reeks. Educated at Eton College and Trinity College, Dermot joined Darley and Co. as a solicitor in 1935. During the Second World War he joined the R.A.F.V.R. as a pilot officer, after which he returned to Dublin to practice at 30 Kildare Street. He later became a Director of Gulf Oil (Ireland). A keen sportsman, he coached successful Trinity VIIIs at Henley and was a member of the Kildare Hunt Committee.
In 1938 he married Patricia ('Tiggy') Kennedy, daughter of Mr and Mrs Edward ('Cub') Kennedy, also of Bishopscourt, Straffan. Whelan's portraits of the couple were exhibited at the Royal Hibernian Academy in Dublin the following year.