== Jacobite pretender == 

 : The longest claimed reign was that of James Francis Edward Stuart (the "Old Pretender"), whose reign as King over the Water lasted 64 years, 3 months and 16 days as the Jacobite pretender to the thrones of England, Scotland and Ireland, then to the thrones of Great Britain and Ireland (17 September 1701 – 1 January 1766). 

 As I misunderstand it, the Jacobites consider(ed) the Act of Union invalid, being enacted by an usurper, and thus deny that there is a throne of Great Britain — so this sentence is a bit like saying a Capetian heir claims the throne of the Fifth Republic. —