The road to the throne for Isabella wasn't without difficulties.

The first offspring of King John's second marriage was Isabella. Her older half-brother Henry, the child of John II and his first marriage, was the heir to the throne. The royal family's marriage was sanctified once more in 1453. A son named Alfonso was born to the Queen.

The lives of King John II's successor, Isabella, and his brother underwent alteration. Henry was crowned king. Even though he didn't get along with his half-siblings, he made sure they had a good education. He dispatched Isabella to Segovia, where she lived in relative ease and comfort.

In 1468, when Isabella's brother Alfonso passed away, everything changed. He designated Isabella as his heir apparent in his will. When she was 13 years old, she was taken to court so that the king could watch over her. Alfonso was the focal point of Henry IV's opposition initially, but after his death in July 1468, the rebellious magnates inevitably turned to Isabella. The noblemen who wanted to seize power in the first place saw this as a great chance. They requested Isabella take the helm of the already formulated revolt.

Isabella decided to handle their conflict on her own. She got together with Henry to talk about the issues and work out a compromise. They agreed that Henry would name her as his successor. Isabella committed to only getting married to someone her brother would approve of.