A legal dispute has revealed that a painting thought to be the world’s most expensive artwork is not the most expensive one after all. Paul Gauguin’s 1892 oil painting “Nafea Faa Ipoipo (When Will You Marry)?” sold for $210 million in 2014, $90 million less than originally reported.

The New York Times and other news outlets reported in 2015 that the painting had been sold by Rudolf Staechelin, a retired Sotheby’s executive, to a Qatari buyer for close to $300 million. If true, that would have been the highest known price for a painting.

Prices in private sales of artwork are often closely guarded secrets, particularly when they reach astronomical levels. On Wednesday, however, a trial began in the High Court in London that revealed the ins and outs of this particular high-stakes art deal, which took nearly two years of negotiations to complete.

In September 2014, Mr. Staechelin sold the painting to a limited liability company run by the British art dealer Guy Bennett on behalf of the emir of Qatar, Sheikh Tamim bin Hamad al-Thani, according to documents submitted to the court by lawyers for the Swiss auctioneer Simon de Pury, who was involved in the dealings. Mr. de Pury’s lawyer wrote that he originally put the buyer and seller in touch. Mr. de Pury, along with his wife, Michaela de Pury, and their limited partnership, have sued Mr. Staechelin and his trust, claiming that Mr. de Pury is owed a $10 million commission on the sale.