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When the campaigns in Africa were over, Afonso V found new grounds for battle in the Iberian Peninsula.
In neighbouring Castile, a huge scandal with political and dynastic implications had arisen.
In 1474, King Henry IV of Castile died without a male heir.
From his two marriages, only a daughter, Joanna of Castile, had been born.
But her paternity was questioned, as rumour said the king was impotent and the queen, Joan of Portugal, had an amorous affair with a nobleman named Beltrán de La Cueva.
The birth of princess Joanna in 1462, openly called La Beltraneja, caused the separation of her parents.
She was never considered legitimate and, when the king was dying, no one took her as a serious contender for the crown.
Her half-aunt, the future Queen Isabella I of Castile, was due to inherit the crown, but Afonso V was keen to interfere with the succession in Castile.
In 1475 he married his niece Joanna, La Beltraneja, whom he considered the legitimate heir to the crown.
Since her adulteress mother was his own sister, Afonso V had not only ambition, but the family honour to protect.
He proclaimed himself King of Castile and León and prepared to defend his wife's rights.
After the indecisive < ref name =" British historian Townsend Miller "> British historian Townsend Miller: “ But, if the outcome of < nowiki > battle of </ nowiki > Toro, militarily, is debatable, there is no doubt whatsoever as to its enormous psychological and political effects ” in The battle of Toro, 1476, in History Today, volume 14, 1964, p. 270 </ ref > Battle of Toro in 1476 against King Ferdinand II of Aragon, the husband of Isabella I of Castile, he went to France to obtain the assistance of Louis XI, but finding himself deceived by the French monarch, he returned to Portugal in 1477 in very low spirits.
Disillusioned and depressed, he fell into a deep melancholy and abdicated in favour of his son, John II.
After this, he retired to a monastery in Sintra where he died in 1481.
His death was mourned in the country, by the people who loved the king, and by the nobles who were starting to fear his successor.

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