Unsurprisingly, stonemason Johnny Beetston had no idea it was worth so much. He'd just found a piece of a broken relief in a quarry and decided to use it to mark the final resting place of his stray cat, Winkle.
When he died, it was sold to a private collector in an auction ten years ago.
But its true value has just come to light when a local historian, Chris Brewchorne, noticed the piece in a front garden and recognised it for what it was - a medieval relief of St Peter.
He immediately knocked on the door and told the owners: "I think you've just won the lottery."
It has now been bought by the Museum of Somerset in Taunton for £150,000 with the help of a Heritage Lottery Fund grant and other donations.
Experts believe that the sculpture could have been created for Somerset's Muchelney Abbey, which is dedicated to St Peter and St Paul. It will go on display on Saturday.
By Catherine Richardson
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