Entitled The Letter, the 10¼ x 13¾in (26 x 35cm) watercolour by the foremost Swedish artist dated from Zorn's spell in England as a young painter after he first arrived in Richmond and then set up a studio in Brook Street, Mayfair.
Signed and dated 1882, it was thought to depict Mary Smith - his favourite English model whom he painted repeatedly over a three-year period before moving on to Paris where he became a notable society portraitist.
It came to Tayler & Fletcher from a deceased estate and, according to the family, had been acquired from the Empress of Austria no less.
The auctioneers took the picture to the Zorn Museum in the Swedish provincial town of Mora, where its authenticity was confirmed by the institution's director, Professor Johan Cederlund.
It was estimated at £20,000-30,000 for the October 27 sale - and every telephone line was booked. Drawing bidding from the US and Europe, as well as from the London trade, it was eventually knocked down to a buyer in the room who flew over from Stockholm, thought to be a dealer acting on behalf of a client.
It is believed the picture will now be heading to a Swedish private museum.
The buyer's premium was 15 per cent.
By Alex Capon