Complex sentence: Marie-Adélaïde was never to see her two younger sons, Montpensier and Beaujolais, who would die in exile before the first Bourbon Restoration in 1814.
Split into simpler sentences: Marie-Adélaïde was never to see her two younger sons, Montpensier and Beaujolais, again. The two of them would die in exile before the Bourbon Restoration in 1814.