For some reason Frau Totenkinder was the only person aware of his existence at first, but Snow soon discovered the truth when fables began turning up dead with the air sucked out of their lungs. As a Zeypher, Ghost feeds on air, and the air in beings supposedly is tastier. Snow secretly sent him away when she became aware of his existence. Due to his very good skills at finding people, Snow told him to find his father and to stay with him. It was Bigby who named him Ghost.
The family has since been reunited. On their fifth birthday, the other six cubs were introduced to Ghost, but were sworn to secrecy as to his existence. Ghost appears sweet, if anything confused since he cannot feel normal things the others do. He's not hungry, thristy or sleepy. But he does tell his siblings he can fart. He's apparently a strong gust of wind when Bigby is about to shovel up the snow on the house sidewalk. Ghost, wanting to help his father blows almost all it up in a strong breeze. Unfortunately it Ambrose, the new Baby Bear and some of the others accidentally get caught up in the wind, and gently get buried in snow.
It appears, that like Ambrose, Ghost could have a greater fate someday. One example could be Frau's predictions. Another could be on the cubs' fifth birthday, when he wanted to play with his brothers' toys. He takes their Jack action figure and puts a sword in it. When they asked why he did it, he says "It felt like it should be there". To which it later shows Jack Horner has a sword stuck in his chest, though that could have been more for comedic reasons.
Bigby and Snow kept Ghost a secret from everyone even Rose, because according to what they told the children. She's not a wolf. But also mostly because of Mr. North, Bigby's father, who has made a habit of killing Zeyphers. However, in Fables #99 , Belleflower reveals to Mr. North of Ghost's existance which leaves him very outraged. Despite the outrage and explaining why he had to dispose of zephyrs, Bigby refused to let him touch his son. In a way to redeem himself with his son and not kill his grandson, North goes out to fight and defeats Mr. Dark by dragging him into his casket of Primordial Winds.