Bump.
After reading again Nek's threads about Richard III winning in Bosworth I imagined the following situation: Richard marries Joana of Portugal, as was intended, and despite her quite old age she gives birth to a male son (let's call him Richard also).
Now, the king John II of Portugal was known as "The Tyrant" by the Portuguese nobility. IOTL he personally killed in 1584 his cousin Diogo, the eldest brother of Manuel of Viseu (the future king Manuel I). Now, let's say that for some reason he decides to kill not only Diogo, but Manuel also. Then the next male heir to the Portuguese throne is Jaime, the 06 years old son of Fernando, Duke of Braganza. Fernando was also killed in 1483 by order of John II, his lands taken to the crown, and his son exiled to Castile.
Considering that John II still dies without children, and not trusting in the Portuguese nobility, he decides to nominate as his heir the son of Joana, his nephew the prince of Wales, the future Richard IV (and Richard I of Portugal).
Now the House of York had just won a succession war for England, and probably has another one to fight for Portugal (of course, assuming that Richard III would seriously consider to take Portugal also).