No offense meant, but Sigi was almost 40 years old when he became king and then reigned for another 42 years. Granted, in 1515 no one could know that Sigi was only halfway through his lifespan. Especially considering Alexander died at 45, Jan Olbracht was 42, but Vladislaus made 60. So theoretically he might have had about another 20yrs, but as I say, in 1515, its unlikely they would think that he has another 33years. He could wait, but he might not. Besides, I know she's a Habsburg and all, but if her mom is Sigi's niece/great-niece marrying her uncle/great uncle is not necessarily gonna do wonders for the Jagiellon gene pool