A grieving widow’s reluctance gave Castile negotiating leverage over Portugal.

Evidence

Diplomatic negotiations to draw up the marriage contract proved remarkably sticky, above all because of one factor: the extreme reluctance of the young lady in question. She had been married to Manuel’s cousin, Afonso, heir presumptive to the throne of Portugal at the time of his death in 1491. Now in 1497 this pious twenty-six-year-old widow was still grief-stricken and resistant to the idea of remarriage. The young Portuguese king, on the other hand, pressed his suit with some urgency (some said for deep romantic reasons and not just because of dynastic ambitions). This put the Portuguese at a disadvantage in their dealings with the Castilian negotiating team (among whom Cisneros was prominent). — L. P. Harvey, Muslims in Spain, 1500 to 1614, 110