Simplify the following text for a Grade 8 native English-speaking person.
Original: York became a unitary authority independent of North Yorkshire on 1 April 1996 , and at the same time Middlesbrough , Redcar and Cleveland and areas of Stockton-on-Tees south of the river became part of North Yorkshire for ceremonial purposes , having been part of Cleveland from 1974 to 1996 .
Simplified: York is now ( since 1996 ) a unitary authority , it is not officially part of North Yorkshire .