He was sometimes popular and sometimes loathed. George’s rule was hampered by mental health problems, though his aides attempted to hide his illness. He was nicknamed ‘Mad King George’. His problems have been attributed to a genetic condition called porphyria, symptoms of which can include severe mental confusion.

George had mild bouts of illness early in his reign, but his health significantly deteriorated from the 1780s. He experienced recurring episodes of severe mental trauma during which he was often physically restrained. Royal courtiers consulted physicians and others offering treatments.

The last two decades of George’s life contained periods of ‘madness’ and remission, but his health continued to decline. The Regency Act of 1811 effectively passed many royal responsibilities to his son George, the Prince of Wales.

Laboratory investigations have shed light on the king’s mental health. Among the Science Museum’s medical collections is an envelope containing hair taken from George III’s head after his death. Analysis found it to be laden with arsenic at a concentration over 300 times that considered toxic. Arsenic is a poison known to trigger porphyria. A likely source of arsenic was James’s Powders, a common medicine regularly given to George. Researchers concluded the arsenic from the medication treating his illness actually made it worse.

Key dates:

1751 - death of his father Frederick Lewis, Prince of Wales. 1760 - begins his reign as king of Great Britain and Ireland and elector of Hanover, following his grandfather, George II. 1761 - married Charlotte of Mecklenburg-Strelitz.

1765 - was unwell for much of the early year, due to constant bickering with his ministers

1783 - the loss of America finally acknowledged.

1786 - stabbed by Margaret Nicholson.

1788 - a serious illness began in the summer with an unpleasant stomach pain ending in his 'madness'.

1795 - stoned in the state coach on his way to Parliament

1800 - shot at by James Hadfield at Drury Lane Theatre.

1801 - suffered a relapse of his 'madness'.

1810 - last public appearance.

1814 - was declared King of Hanover at the Congress of Vienna.