sentences:  Her last brother to hold the title of Earl of Pembroke died without legitimate issue, and the title was passed down through the family of Isabel's younger sister Joan.Her sisters married, respectively, the Earls of Norfolk, Surrey, and Derby; the Lord of Abergavenny and the Lord of Swanscombe.On her 17th birthday, Isabel was married to Gilbert de Clare, 4th Earl of Hertford and 5th Earl of Gloucester, who was 20 years her senior, at Tewkesbury Abbey.