The Shore Beyond (слэш)

Twenty-two-year-old Harry Potter and his five-year-old godson, Teddy, fall headfirst into a 1991 that was never meant to exist.
Harry’s parents are alive. His eleven-year-old self is at Hogwarts. And Harry is now his Defence Against the Dark Arts professor.
With Voldemort still moving in the shadows, keeping his identity secret is difficult enough. It becomes even harder when Harry begins to suspect that their arrival in the past is not the only thing that has gone wrong with time.
Severus Snape is one of the few people who knows the truth and has kept a wary, disapproving eye on Harry from the start.
Harry has been dealing with Snape since he was eleven. What could Snape possibly have left to surprise him with?
Quite a lot, as it turns out.