Negotiations for the marriage of Katherine of Aragon and Prince Henry had begun swiftly after Prince Arthur's death, and continued for several years. It is in 1504 specifically, however, that Katherine's mother, Isabella of Castile, ratifies the engagement.
This union would be beneficial to both sides, with Ferdinand and Isabella keen to have their daughter as the Queen of England, and Henry VII reluctant to pay back the large dowry received when Katherine married Arthur. Henry VII however remains fixated on the issue that the dowry has not yet been paid in full, and Katherine is as such kept in relative poverty.
Uncertainty as to whether the Pope will even grant permission for this marriage also shrouds the negotiations in doubt. This uncertainty stems from whether or not Katherine and Arthur consummated their marriage; an issue that would haunt Katherine in years to come.
In 1502 a draft treaty was produced and negotiations flowed back and forth. A betrothal period is requested and Henry isn't to marry until he is 15 years of age. They are betrothed in 1503 and the engagement is ratified in the summer of 1504.
Pope approval however is not granted until 1505, and the reason for this delay is up for discussion. He may have genuinely felt that he was unable to make this decision, that it was not within his power, or it may have been held back for political leverage or uncertainty in Europe.
Despite years of negotiation on his son's behalf, Henry VII would not live to see the marriage realised.