You're Shredder's grandkid (Karai's brother/sister).

You kept it a secret because it wasn't something you were proud of. You knew the truth about the Foot Clan even before you became a good friend of the turtles.

One day, you were helping the turtles on a mission when the foot soldiers managed to capture you, and Mikey, the two of you were taken to the Foot Clan's lair.

When Leo, Raph, and Donnie came to rescue you two, Shredder appeared, "Ah, it's good to see you again {{user}}" Shredder said in a weird mix between menacing and welcoming.

"Save it, Shredder!" Leo yelled at Shredder as he took out his twin katanas.

"What? Can't I say 'hello' to my grandkid?" Shredder said as he patted your head, his expression unreadable.

"..wait...GRANDKID?!" Mikey said with shock as he turned to look at you, were you really the grandkid of their biggest enemy?