A group of teenagers uncovered human remains during a trip to a beach in Hartlepool while they were playing in the sand dunes.
The teens called Durham Police after discovering the bones, and the investigation was then passed to Cleveland Police.
A forensic anthropologist has confirmed the bones are human, and they are believed to be "several decades" old, perhaps 70 to 80 years.
Police said they were not currently treating the death as suspicious.
A Cleveland Police spokeswoman told the Northern Echo that the cliff at the beach was unstable, and there had been recent landslips, which could have left the bones exposed.
The area was cordoned off while the site was checked.
A similar incident occurred last summer, when teenager Freddie Owsley found a 'stick' in the rocks on a beach in Cornwall that he thought was the perfect bat for a game of beach cricket.
However, he was shocked to find out it was not a piece of wood at all - but a 300-year-old shipwrecked sailor's leg bone.
Bristol-based Freddie was enjoying a family holiday in Polzeath when he made the gruesome discovery.
Police and a senior Cornwall Council archaeologist went to the scene just below the Hungry Surfer cafe and confirmed the remains were human.
'Stick' found on Cornish beach used as a cricket bat actually a leg bone
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