Femme endormie is a 1931 charcoal drawing by Pablo Picasso that is to this day largely unseen. The portrait of his lover and muse, Marie-Thérèse Walter, was personally kept by the artist until his death in 1973, and now it will be auctioned off by Sotheby’s London this month, with an estimated selling price between $7 million to $12 million USD.

17-year-old Walter was Picasso’s muse and lover who inspired numerous paintings, sculptures and drawings, some considered his greatest works. He first fell for her when he saw her through the window of Galeries Lafayette in Paris in 1927. The painting, created when the affair was still a secret, “is just wonderful, it looks back to the great drawings of the Renaissance yet it is so incredibly modern and free and spontaneous and direct,” says Helena Newman, head of Sotheby’s Impressionist and Modern Art department. “It is like you are looking over his shoulder as he is drawing it.”

Taking place on July 28, Sotheby’s evening sale will also include works by artists Wassily Kandinsky, Fernand Léger, Alberto Giacometti, Marc Chagall, and Jean Arp.