sentences:  He had a younger brother, Thomas de Mowbray, 1st Duke of Norfolk, and three sisters, Eleanor, Margaret and Joan (for details concerning his siblings, see the article on his father, John de Mowbray, 4th Baron Mowbray).He was styled 'cousin' by John of Gaunt, 1st Duke of Lancaster.At the death of his mother in 1368, Mowbray is said to have become Baron Segrave.