Michael is Kitty Pryde's child with Colossus in an illusion, in Astonishing X-Men 17.
When Perfection, posing as Emma Frost, takes out the entire team with telepathy, Kitty is sent into a delusion where she gives birth to a child who is then taken away from her for eighteen months. In the illusion, the X-Men justify this by saying that Michael has a "great and terrible" power and must be contained. After about two years, she finally gets past their defenses and opens the box they're keeping Michael in, but instead finds a huge greenish grub that actually contains the essence of Cassandra Nova.