Fullmetal Alchemist: Brotherhood - episode 40 - 16 Jan, 2010

Olivier goes to Central, where she admits to killing Raven and convinces Bradley to let her take his place. Hawkeye uses a coded message to tell Roy Mustang that Selim is a homunculus. Meanwhile, Father dreams of ancient Xerxes, where Hohenheim had been raised as a nameless slave, known only as Number 23. There, Hohenheim had met Homunculus, a being in a flask who was created from his blood, which gave Hohenheim his current name and taught him the basics of alchemy. One night, Homunculus had been summoned by the King of Xerxes, who asked Homunculus to tell him the secret for immortality. Homunculus had tricked the king into making a gigantic transmutation circle, using the whole country as a sacrifice, while it and Hohenheim stood at the center of the circle. When Hohenheim had awakened, everyone else in Xerxes was dead, except for Homunculus. It had created a body shaped like Hohenheim for itself, then becoming known as Father. Back in the present, after Hohenheim awakes from this shared dream, he runs into Izumi and Sig. When Hohenheim notices that Izumi committed the ultimate sin, he rearranges her organs so that her blood can flow better. After this, Hohenheim tells Izumi and Sig that he is the philosopher's stone in human form. (Source: Wikipedia)