It was one of Devon's oldest trees and the centrepiece of Phear Park, Exmouth, which is itself only 100 years old this summer.
The great oak which had been attacked by a fungus for years toppled over on Sunday night despite only light winds blowing.
It had been failing for some time and is thought to have died as a result of its age.
The trunk snapped off with most of the roots left in the ground, where a huge hole opened up.
The so-called 'Champion oak' was donated to the people of Exmouth by the Phear family after the Second World War.
While its exact age is not known, since the first Lucombe oak was grown by William Lucombe in the 1760s, it could be up to 250 years old.
East Devon District Council gardeners now have the task of deciding what to do with the trunk.
Steve Gazzard, 60, who was born and brought up in Exmouth and climbed the tree as a youngster with his brother Martin, said: "It is a terrible blow.
"She really was an old faithful and we were all looking forward to the coming weeks when she would have looked her best, surrounded by a host of daffodils.
"I have seen her grow in the past 60 years. Bicton College collected some seeds from her a few years ago and I am hoping that perhaps offspring could be planted in the park to keep the family going.
"We will need a mature tree planted thereabouts as a replacement and I think it would be a good idea if we could keep the fallen trunk as some kind of climbing frame for the young people."