Who was the monarch at the time of Waterloo?

The monarch at the time of the Battle of Waterloo in 1815 was King George III of the United Kingdom. He had been on the throne since 1760, but due to his deteriorating mental health, his son, the Prince of Wales, served as regent from 1811 onwards. The battle was a pivotal moment in the Napoleonic Wars, leading to the defeat of Napoleon Bonaparte.