...after that had that damned bishop of his declaring who King Edward had taken another wife before the mother of his children! The confused Englishmen had believed their words and now the bastard had declared Archduchess Elisabeth ... as illegitimate ...
I never thought of that - that in declaring Edward IV's marriage invalid, RIchard may clear his way to the English crown, but would also give great offense to the husband of any of Edward's daughters.
There are a lot of things to spin off of this.
For instance, WI it's a fair cop? I.e. there is solid proof that Edward really did marry Eleanor Talbot and Elizabeth really is a bastard? (As are the Princes.) Let's say Richard hangs back, and doesn't rush to seize the crown. Instead he waits for opinion to swing round to acceptance, so the scandal can't just be passed off as an usurper's lie. Maximilian will still be upset, but can't blame Richard - it's really Edward's fault. And how the heck do the Habsburgs deal with this.
Another thought: could there be a parallel situation at other times? Henry VIII, in getting his marriage to Catherine annulled, made Mary a bastard. WI she had been married overseas first? That would need a son for Henry who lives at least till Mary's marriage (as the heir presumptive would not be married abroad). But the son might die later, and Catherine continues to have stillbirths or miscarriages, leading Henry to conclude that the marriage is accursed and he needs to remarry for a male heir. But if he acts as OTL, he's made... the Queen of Portugal? a bastard.
What other cases of retroactive royal bastardy were possible?