Complex sentence: In the meantime, Louis XII had succeeded to the French throne, and who claimed the rights both to the Duchy of Milan as a grandson of Valentina Visconti, and the Kingdom of Naples as heir to the House of Anjou.
Split into simpler sentences: In the meantime, Louis XII had succeeded to the French throne. Louis claimed the rights both to the Duchy of Milan as a grandson of Valentina Visconti, and to the Kingdom of Naples as heir to the House of Anjou.