The bus – Eastern National FLF LWC661C – started its service in 1965.
It was withdrawn from service in 1980 and passed over to Southdown Motor Services in Brighton where it was used for spare parts.
In September 1981 it headed to Drusillas Zoo Park where it has delighted visitors until this week.
Donated to the West of England Transport Collection, the Drusillas bus joins 70 other vintage and classic buses.
Daniel Shears, the collector, said, “I was put in contact with Peter Moon at Drusillas by a friend who thought the bus would be of interest to my collection. Once I saw the pictures I had to save it!
“I purchased a running example a few years ago and thought it might be a good source of spares to restore the one I have but now I have had a good look at it I might well find an engine and gearbox and get it roadworthy again.”
Over the years the bus has had many faces and purposes. It started as The Discovery Bus, got a Thomas the Tank Engine makeover, and then became the Zoo Lab with the lower deck providing an activity space for children and the upper deck serving as a lecture theatre.
Drusillas deputy managing director Cassie Poland, said, “The Drusillas bus has been a fond favourite of our visitors for longer than I’ve even been alive!
“It’s a little sad to be letting go of a piece of the park’s history, but we are so thrilled that the bus has gone to someone so passionate who has plans to restore it to its former glory.
“The space now provides us with a great opportunity to continue developing the visitor experience, so keep a look out for announcements on what’s coming next!”