Five years after their marriage, the Queen was said to have given birth to a daughter, whom Henry declared should be his successor, in lieu of his young brother Alfonso (John's son, by a second wife, Isabella of Portugal).

This child the nobles refused to receive, believing and declaring that she was not Henry's daughter, and arrogated to themselves the right of trying and passing sentence on their Sovereign, who, by his weak, flagitious conduct had, they unanimously declared, forfeited all right even to the present possession of the crown.
The confederates, who were the very highest and noblest officers of the realm, assembled at Avita, and with a solemnity and pomp which gave the whole ceremony an imposing character of reality, dethroned King Henry in effigy, and proclaimed the youthful Alfonso sovereign in his stead.

All present swore fealty, but no actual good followed: the flame of civil discord was re-lighted, and raged with yet greater fury; continuing even after the sudden and mysterious death of the young prince, whose extraordinary talent, amiability, and firmness, though only fourteen, gave rise to the rumor that he had actually been put to death by his own party, who beheld in his rising genius the utter destruction of their own turbulence and pride.

Be this as it may, his death occasioned no cessation of hostilities, the confederates carrying on the war in the name of his sister, the Infanta Isabella.

Her youth and sex had pointed her out as one not likely to interfere or check the projects of popular ambition, and therefore the very fittest to bring forward as an excuse for their revolt.