William (jr) was born in 1185. William (jr)'s father is William Munchensy and his mother was Eveline de Clare. His maternal grandparents are Roger de Clare and Maud de Saint Hilary. He had a brother and three sisters, named Warin, Hawise, Alice and Cecily. He was the oldest of the five children. He had a half-brother named John. He died at the age of 23 on April 6th, 1208.