It is through the dark-haired Gladys, who married Ralph Mortimer,
that the kings of England can trace their descent from the House of
Cunedda.

Llywelyn's last great task was to make relations between England and
Wales relations of peace and amity. During his long reign, he saw
three kings on the throne of England--the crusader Richard, the able
John, and the worthless and mean Henry III. It was with John that he
had most to do, the king whose originality and vices have puzzled and
shocked so many historians. John helped him to crush Gwenwynwyn,
then helped the jealous Welsh princes to check the growth of his
power. Llywelyn saw that it was his policy, as long as John was
alive, to join the English barons. They were then trying to force
Magna Carta upon the King, that great document which prevented John
from interfering with the privileges of his barons. In that document
John promises, in three clauses, that he will observe the rights of
Welshmen and the law of Wales.

When John died in 1216, and his young son Henry succeeded him, the
policy of England was guided by William Marshall Earl of Pembroke.
William Marshall was one of the ministers of Henry II., and by his
marriage with the daughter of Strongbow, the conqueror of Ireland, he
had become Earl of Pembroke. It was with him that Llywelyn had now
to deal. He was too strong in Pembroke to be attacked, but his very
presence made it easier for Llywelyn to retain the allegiance of the
chiefs who would have been in danger from the Norman barons if
Llywelyn's protection were taken away. In 1219 the great William
Marshall died; and changes in English politics forced his sons into
an alliance with Llywelyn.