Who was the father of Isabel Marshal's husband>
Isabel Marshal:  She was the wife of both Gilbert de Clare, 4th Earl of Hertford and 5th Earl of Gloucester and Richard, 1st Earl of Cornwall (son of King John of England). Richard, 1st Earl of Cornwall: Richard (5 January 1209 – 2 April 1272), second son of John, King of England, was the nominal Count of Poitou (1225-1243), Earl of Cornwall (from 1225) and King of Germany (from 1257).
John, King of England