Then, in the 1940s, John Pope-Hennessy, the director of the Victoria and Albert Museum in London, realised that the museum owned a work of art that was exactly the thing that was missing from the Brancacci Chapel. It was a thin, almost flat marble slab delicately carved with the scene of Jesus giving "the Keys" to Peter. It was just the right size to make the front of an altar. And although it could not be proved, it was almost certainly carved by Masaccio's friend, Donatello.