So, the casting of Hephaistion was pretty much settled before the casting process even started...
How did Jared get the job? This is how it officially went down:
early May 2003: casting notice goes out for Hephaistion
"It was my first audition since Panic Room, which was a couple of years before, and I was completely petrified," confesses Leto. "There were 50 other people there to meet Oliver, and it was incredibly intimidating. But when I auditioned, thankfully, he saw something in me that he thought might be right for Hephaistion. I'll be eternally grateful to him for believing in me and giving me this experience. He works harder than any other person on the set. He's obsessed, he's a mad genius, like Van Gogh or Beethoven. He's taught me a lot on this film, and I'll carry those things with me for the rest of my career."
early August 2003: announcement.
early July 2003: Rumors that Jared had already secured the role despite "hundreds of young Irish actors" reading for Stone in June. Jared joined Stone, Colin and "some other actors" in Dublin at the bar in Bono's hotel. Hanging with U2, of course.
April 2003: is when Jared (officially split from Cameron Diaz) says he knew he had the movie and was growing his hair out. And he did. He did.
Maybe he's just a little confused? Yet it's obvious he was cast long before it was announced, even before the casting notice, and while people were still auditioning for the role. Pretty much the same with Angelina. She was set. Stone wanted her to play mum Olympias even though she was the same age as Colin. I love this outrageous movie. It deserves a movie about its making.