|Wedding portrait of Isabella and Ferdinand (1469)|
She was born on 22 April 1451, and there was never any speculation that she might one day rule Castile. She had an older half-brother, Henry, who was 26 when Isabella was born. When Henry succeeded their father (John II of Castile) in 1454, Isabella and a younger brother, Alfonso, were sent with their mother to live in a run-down castle in another region, away from the capital. Despite the simple accommodations, Isabella was raised by her mother to be educated and devout. In 1462, Isabella and Alfonso were brought back to the royal palace in Segovia. Isabella was put in the queen's household where her education became more extensive.
When Alfonso died in 1468 (probably from plague), Isabella inherited his possessions. Castilian nobles wanted to use Isabella as a fiscal point to dethrone Henry, but Isabella wasn't having it. She negotiated a settlement with Henry: she would not become a threat to his throne, he would name her heir-presumptive. Moreover, he would not force her into a political marriage of which she did not approve, but she would not marry without his consent.
Years earlier, at the age of 6, she had been betrothed to Ferdinand, son of the king of Navarre. Ferdinand's father and Isabella's brother were trying to make a firm alliance between their two countries, but their relationship did not last. Years later, however, after numerous other potential betrothals in which Isabella invoked her old agreement to avoid a forced marriage, she contacted Ferdinand secretly and expressed her wish to marry him.
There was a problem with consanguinity, the two being second cousins, but a papal bull from Pius II—thanks to the efforts of Cardinal Rodrigo Borgia (later Pope Alexander VI)—gave them a dispensation. Isabella, on the pretense of visiting her brother's tomb, left Henry's court. Meanwhile, Ferdinand crossed into Castile while in disguise. The two met up at the town of Valladolid.* Having successfully outmaneuvered her brother, the pair were wed on 19 October 1469. Isabella was 18, Ferdinand was 17.
*They later made valladolid their capital city. Christopher Columbus died there.