Paddy Roy Bates, who occupied an abandoned fort in the North Sea and declared it the sovereign Principality of Sealand — with himself as its prince — has died at age 91.

Bates' son Michael says his father died Tuesday at a care home in Leigh-on-Sea in eastern England. He had been suffering from Alzheimer's.

In the 1960s, Bates moved with his family to a disused World War II fort about seven miles (13 kilometers) off England's east coast. He proclaimed it the Principality of Sealand, with himself as Prince Roy.

Bates gave Sealand its own flag, passport, stamps, coins and national anthem. It claimed to be the world's smallest sovereign state, though it was not internationally recognized.

Bates is survived by his wife Joan, son Michael and daughter Penny.