[1]: 41 At the time of his birth, Castile was under control of Álvaro de Luna, Duke of Trujillo, who intended to select Henry's companions and direct his education.

After the victory at Olmedo, Álvaro de Luna's power waned, and Prince Henry and Juan Pacheco's influence grew.

His other main concerns were the possibility of intervention from King John II of Navarre, establishing peace with France and Aragon, and pardoning various aristocrats.

King John II resumed his interference in Castillian politics, supporting the aristocratic opposition to Juan Pacheco's ambitions.

With the support of the King Henry, Pacheco moved to seize Álvaro de Luna's assets, but his widow allied herself with the Mendoza family, causing a division among the aristocracy.

[5][6][7] They raised a large number of noblemen, took control of expenditure, and gained the acceptance of Alfonso of Castile, the King Henry's half-brother and Prince of Asturias.

[8] To counteract King John II's politicking, Henry IV reacted by invading Navarre in support of Charles, Prince of Viana.

[1]: 55  The campaign was a military success, but King Henry made peace with the League of Nobles in August 1461 to ward off the power of the Mendozas, which had allowed John II to intervene in Castile.

King Henry's intervention was framed as a rivalry between him and John II, making Catalonia an unstable point in the Crown of Aragon.

The first marital approaches were made in December of that year, although the negotiations were long and the proposal wasn't definitively agreed until February 1455.

On 28 February 1462, the queen gave birth to a daughter Joanna la Beltraneja, whose paternity came into question during the conflict for succession to the Castillian throne when Henry died.

The first attempt was when the six-year-old Isabella was betrothed to Ferdinand, son of John II of Navarre (a cadet branch of the House of Trastámara).

But a conflict with the nobility was created when Beltrán de la Cueva deposed Juan Pacheco, the Marquis of Villena, and his brother Pedro Girón, Master of Calatrava from Henry's court.

[11]: 185 [17] This caused a change in alliances: Mendoza began to support the king, and Pacheco revived the Aristocratic League aimed at eliminating the influence of Beltrán de la Cueva.

The nobles in league against him conducted a ceremonial deposition-in-effigy of Henry outside the city of Avila and crowned Alfonso as a rival king.

Shortly thereafter at the negotiation of Toros de Guisando, in which she and her allies received most of what they desired, Henry agreed to exclude Joanna la Beltraneja from the succession, and to recognize Isabella as his official heir.

Though Henry continued to resist this decision when possible, his actions were ineffective, and he remained at peace with Isabella for the rest of his reign.

Though many contemporary historians and chroniclers believed Henry was impotent or homosexual,[19] the royal chronicles of his reign were all written or revised during the reign (and under the influence) of Isabella I, his half-sister and ultimate successor, whose strong interest in proving Joanna illegitimate renders these accounts at least partially suspect, in addition to the fact that female prostitutes testified to having intercourse with Henry.

The doubt of her legitimacy as an heir, the weakness of the king, the adultery of the queen, and the unruliness of the nobility all set the stage for a struggle for succession after Henry's death.

After a long period of conflict between the rival factions, Henry finally agreed to name Isabella his successor, in Guisando (Ávila), provided she allow him to arrange her strategic marriage.