On 29 Sep 1308 (possibly 30th) in a Siblings Marriage de Clare siblings married de Burgh siblings at Waltham Abbey [Map] in the presence of King Edward II of England (age 24).

John Burgh (age 22) and Elizabeth Clare Lady Verdun (age 13) were married. She the daughter of Gilbert "Red Earl" Clare 7th Earl Gloucester 6th Earl Hertford and Joan of Acre Countess Gloucester and Hertford. He the son of Richard "Red Earl" Burgh 2nd Earl Ulster (age 49) and Margaret Burgh Countess Ulster. She a granddaughter of King Edward "Longshanks" I of England.

Gilbert de Clare 8th Earl Gloucester 7th Earl Hertford and Matilda Burgh Countess Gloucester and Hertford (age 20) were married. She by marriage Countess Gloucester, Countess Hertford. She the daughter of Richard "Red Earl" Burgh 2nd Earl Ulster (age 49) and Margaret Burgh Countess Ulster. He the son of Gilbert "Red Earl" Clare 7th Earl Gloucester 6th Earl Hertford and Joan of Acre Countess Gloucester and Hertford. He a grandson of King Edward "Longshanks" I of England.