Through a secret agreement in 1912, Berenson enjoyed a close relationship with Joseph Duveen, the period's most influential art dealer, who often relied heavily on Berenson's opinion to complete sales of works to prominent collectors who lacked knowledge of the field. Berenson was quiet and deliberating by nature, which sometimes caused friction between him and the boisterous Duveen. Their relationship ended on bad terms in 1937 after a dispute over a painting, the "Allendale Nativity" (a.k.a. the "Adoration of the Shepherds" now at the National Gallery in Washington), intended for the collection of Samuel H. Kress. Duveen was selling it as a Giorgione, but Berenson believed it to be an early Titian. The painting is now widely considered to be a Giorgione. Besides assisting Duveen, Berenson also consulted for other important art dealerships, such as London's Colnaghi and, after his breakup with Duveen, New York's Wildenstein.