Discovered during a routine house call, the rare 10 x 4in (25 x 10cm) pen and ink drawing was offered by Peter Francis of Carmarthen on July 24.
It had come to the vendor through André Raffalovich, a family friend and one of Beardsley's benefactors and had remained wrapped in tissue paper for several decades.
Four phone lines were active on the day, but it came down to two bidders who took it well over the attractive £10,000-15,000 estimate, selling to Rupert Maas of London's Maas Gallery for £40,500.
The current record for a Beardsley work is The Climax, an illustration for Oscar Wilde's Salome which took $180,000 at Boston auction house Skinner's in November 2008.
The buyer's premium was 20%.