https://wccftech.com/fortnite-halo-master-chief/

Yesterday it was leaked that God of War’s Kratos will be bringing his mad dad energy to Fortnite soon, but it turns out he’s probably not the only console mascot making his way to the Island. Last evening some Halo-related Fortnite images, including Master Chief himself, popped up on 4chan. Now, 4chan often isn't a very reliable source, so take this with a grain of salt, but various Fortnite insiders and dataminers, including Twitter user Mang0e, are vouching for the leak.

I've tracked the source of this original image to 4Chan.