POV: France finds out Philip of Spain and Mary Tudor had a child, and he's about to inherit both the Spanish and the English crown
Basically, if Philip and Mary had a child, he would have inherited the throne of his mother in 1558, and as prince Charles of Spain (Philip's first son) died aged 23, that would have made him heir to the Spanish throne. No English support means Low Provinces revolt suppressed, which also means no Eighty Years War, and so no Netherlands.
Basically, France would be surrounded by enemies.