Supernatural / Harry Potter crossover

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Hello, lovely people :) Looking for a fic I read a while ago. Gabriel sends Sam and Dean into the HP universe. At first, they have no idea what's going on and try to kill Remus but then they find Sirius and are horrified when they find out they've been trying to kill Professor Lupin.

By the end, everything is alright and the Harry Potter books get a lot less sad.

Short-ish (probably around 3-4k).

Thanks in advance!