A newly-identified sketch of Leonardo da Vinci is to go on public display for the first time at Buckingham Palace. The drawing of a bearded man is believed to be one of only two surviving portraits made during the artist’s life time. Martin Clayton, head of prints and drawings at the Royal Collection, uncovered the image while examining papers stored in Windsor Castle.

He identified it as a study of Leonardo made by an unidentified assistant shortly before the artist’s death, aged 67, in 1519. The only other contemporary portrait was made at around the same time by Leonardo’s pupil Francesco Melzi, the expert said. Another drawing in Turin is widely believed to be a “self-portrait” of the Italian master but Mr Clayton and other experts have questioned the claim.