The granite relic was given to Bronwen Hickmott’s parents by a tea planter who returned to Britain from Sri Lanka in the 1950s.
Mrs Hickmott inherited the 2.4m-long (8ft) stone from her mother and father and began using it as a doorstep at her home in Exeter, Devon – affectionately calling it ‘the pebble’.
But an expert who spotted the one tonne stone in a photograph later confirmed it was actually a Buddhist temple step – up to 1,300 years old.
It was put up for auction with a pre-sale estimate of £30,000 to £50,000 but sold yesterday for ten times as much – £553,250.
Mrs Hickmott said she was ‘over the moon’ at the sale, and that rival auction house Sotheby’s had previously shown no interest in helping her research the origin of what she called ‘The Pebble’.
And she told how she was also turned down by producers of BBC1’s Antiques Roadshow.
She likened the response of Sotheby’s and the BBC producers to that of shop staff in hit film Pretty Woman who famously refuse to serve Julia Roberts – and miss out on a fortune when she goes on a spending spree.
Mrs Hickmott said: ‘They have had a Pretty Woman moment. It was a big mistake. I bet they are kicking themselves now.’
She added: ‘We are over the moon. We did not have a clue what ‘The Pebble’ would sell for.
‘It was very exciting and as the amount increased we were left speechless and holding our breath.
‘I have loved ‘The Pebble’ virtually all my life. I always knew it was something special – but never knew how special.