Llewelyn was born in 1870 to
Sir John Dillwyn-Llewelyn, 1st Baronet and his wife who was the daughter of
Sir Michael Hicks Beach, 8th Baronet. His father was
High Sheriff of Glamorgan, Mayor of Swansea and MP for
Swansea. He married in 1893 Katherine Minna Venables, daughter of Richard Lister Venables. Following this marriage, the
Llysdinam estate came into the family and Sir Charles assumed the additional surname of Venables. He established a wildlife centre on the estate, today run by
Cardiff University. Sir Charles' son, Sir
Michael set up the Field Centre at Llysdinam in 1970 which was run by Cardiff University until 2010. His daughter, Agnes Barbara Dillwyn-Venables-Llewelyn, married naval officer
Cedric Holland on 15 June 1925. == Military and political career ==