PIACENZA, Italy (AP) — Art experts have confirmed that a painting discovered hidden inside an Italian art gallery’s walls last month is Gustav Klimt’s “Portrait of a Lady,” which was stolen from the gallery nearly 23 years ago.

The authentication of the painting announced Friday solved one of the art world’s enduring mysteries — where did the missing work end up? — but left several questions unanswered, including who had taken it and whether it ever left the museum’s property.

A gardener at the Ricci Oddi Modern Art Gallery in the northern city of Piacenza who was clearing away ivy noticed a small panel door on a wall outside and opened it. Inside the space, he found a plastic bag containing a painting that appeared to be the missing masterpiece.