A History of ThePlantagenets, Vol II, The Magnificent Century, Thomas B Costain, 1951, Doubleday & Co
p242: "...In 1253 [Richard De Clare's] ten-year-old son Gilbert, called the Red because of the color of his hair, was married to Alice of Angouleme, daughter of Guy de Lusignan and therefore a stepniece of the King. The Earl of Gloucester took this alliance with royalty seriously, but as he was intensely proud and most tenacious of his rights as a leading peer, Henry had never been able to count on his support..."
The New Columbia Encyclopedia, 1975, p1094, Gloucester Gilbert De Clare 8th Earl of: "1243-1295, English nobleman, son of the 7th Earl. He married (1253) Alice de Lusignan, niece of Henry III, and succeeded to the Earldomin 1262... His first marriage was annulled, and in 1290 he married Edward's daughter Joan..."