I had my suspicions as to who the "Her" was all along, but they weren't confirmed until I read Billy Joel's biography "The Life and Times of an Angry Young Man." Billy talks about when he first started dating her. He says that she was the first person he could ever just talk to, and they would spent hours just talking - and that was the basis for "Tell Her About It." It's simply about the moment he realized that one could actually have a soul mate. Joel met her in 1982, married her in 1985 and they divorced in 1994. The "Her" was Christie Brinkley.