Lionel Percy Smythe (1839-1918) was Wyllie's older half-brother and the eldest of three illegitimate children that their mother, Katherine Benham, a singer, had with Percy Smythe, 6th Viscount Strangford (though the family always claimed a marriage).
He was born in London on 4 September 1839 and spent his early years in France, where his younger sister and brother were born, though the family returned to London in 1843 and lived in Gloucester Crescent, Camden.