The county was subject to significant boundary reform in 1974 that removed Liverpool and Manchester and most of their surrounding conurbations to form the metropolitan counties of Merseyside and Greater Manchester. The detached northern part of Lancashire in the Lake District, including the Furness Peninsula and Cartmel, was merged with Cumberland and Westmorland to form Cumbria. Lancashire lost 709 square miles of land to other counties, about two fifths of its original area, although it did gain some land from the West Riding of Yorkshire. Today the county borders Cumbria to the north, Greater Manchester and Merseyside to the south and North and West Yorkshire to the east; with a coastline on the Irish Sea to the west. The county palatine boundaries remain the same[clarification needed] with the Duke of Lancaster exercising sovereignty rights, including the appointment of lords lieutenant in Greater Manchester and Merseyside.
Try to answer this question if possible (otherwise reply "unanswerable"): When did the current Duke of Lancaster start his reign?
unanswerable