If this came as a surprise to Dumbledore, then he hadn’t seen Snape’s doe Patronus for years, or perhaps ever before. As far as we know, the only people who ever saw the doe were Sirius, Dumbledore, Harry, and Ron. Dumbledore worked with Snape, depended upon him, but never asked him the private source of his growing strength. Perhaps he assumed that with time, Snape’s memories of Lily would have faded or been replaced. But Snape’s Patronus is powerful and effortless: it must be never far from his mind that all his protective powers have grown from that one original source, the
