A rare Michelangelo drawing is expected to sell for up to £5 million in London next month, according to Christie's.
The male nude is one of only 24 sheets relating to The Battle of Cascina, an uncompleted work described by the auction house as "one of the greatest Western masterpieces that never was".
The only time the drawing has been seen in public was in Vienna last year.
Benjamin Peronnet of Christie's said it offered "a glimpse into the mind of a genius at the peak of his powers".
Michelangelo was commissioned to commemorate the 1364 Battle of Cascina in a fresco at Florence's Sala del Gran Consiglio in 1504.
Leonardo da Vinci was commissioned at the same time to paint the Battle of Anghiari of 1440 on an opposite wall.
Neither piece was completed and only survive through engravings and sketches.
The sketch - the only study for the fresco in private hands - will go under the hammer on 5 July.