In 1923, Berenson was called to give expert witness in a famous case brought by Andrée Hahn against Duveen. In 1920 Hahn wanted to sell a painting that she believed to be a version of Leonardo's "La belle ferronnière" and whose authorship is still debated. Duveen publicly rejected Hahn's Leonardo attribution of the painting, which he had never seen. Consequently, Hahn sued him. In 1923 Hahn's painting was brought to Paris to be compared with the Louvre version. Duveen mustered Berenson's and other experts' support for his opinion, dismissing Hahn's painting as a copy. At the trial in New York in 1929, where the expert witnesses did not appear, the jury was not convinced by Berenson's Paris testimony, in part because, while under cross-examination there, he had been unable to recall the medium on which the picture was painted. It was also revealed that Berenson, as well as other experts who had testified in Paris, such as Roger Fry and Sir Charles Holmes, had previously provided paid expertise to Duveen. While Duveen, after a split verdict, ended up settling out of court with Hahn, the whole story damaged Berenson's reputation.