Both Naples and Sicily were conquered by a Spanish army during the War of the Polish Succession in 1734, and Charles, Duke of Parma, a younger son of King Philip V of Spain was installed as King of Naples and Sicily from 1735. When Charles inherited the Spanish throne from his older half-brother in 1759, he left Naples and Sicily to his younger son, Ferdinand IV. Despite the two kingdoms being in a personal union under the House of Bourbon from 1735 onwards, they remained constitutionally separated.