Aaron is one of Neptunes decendants and is also one of Emily's best friends.
Aaron is first introduced in the third book. Emily discovers him in the castle in the mist when she opens a door, bumping in to him. He is tall, about a few years older then Emily and Shona, and wears mostly black because of his fathers recent death. Together, he and Emily find the pearl ring that goes with the diamond ring, breaking the horrible curse set by Neptune.