Their conversion was reinforced after 1810. In that year, George III, who had suffered periodically from mental instability (possibly due to porphyria), became permanently insane and spent the remaining 10 years of his life unable to discharge his duties. The Prince Regent was prevented from using the full powers of kingship. The regent became George IV in 1820, but during his 10-year reign was indolent and frivolous. Consequently, for 20 years the throne was virtually vacant and Tory Cabinets led by Tory prime ministers filled the void, governing virtually on their own.