The Navarrese Civil War of 1451–1455 pitted John II of the Kingdom of Navarre against his son and heir-apparent, Charles IV. When the war started, John II had been King of Navarre since 1425 through his first wife, Blanche I of Navarre, who had married him in 1420. By the marriage pact of 1419, John and Blanche's eldest son was to succeed to Navarre on Blanche's death. When Blanche died in 1441, John retained the government of her lands and dispossessed his own eldest son, Charles (born 1421), who was made Prince of Viana in 1423. John tried to assuage his son with the lieutenancy of Navarre, but his son's French upbringing and French allies, the Beaumonteses, brought the two into conflict. John was supported by the Agramonteses.