Beach walker Mandy Ewington was strolling along the seafront when she looked up and saw two bones poking out of a vertical cliff face.
She took a picture of the leg bones and sent them to top archaeologist Karl-James Langford.
Mr Langford, 39, said “I thought she must have been mistaken but I went down and thought bloody hell, this is amazing!”
“You can clearly see a grave has been eroded into the sea.
“What is fascinating is that two leg bones have been slowly revealed as the cliffs has eroded in the bad storms.
“It was an amazing find by Mandy – those legs have been there for around 800 years.”
University lecturer Mr Langford said the cliffs at Monknash, near Bridgend, South Wales, was a burial ground for monks in the Middle Ages.