The Fortnite X Batman collaboration has officially been revealed during a livestream on the Fortnite YouTube channel.
In the v10.31 Fortnite update, dataminers leaked a number of files which all but confirmed we would be getting a Fortnite X Batman collaboration in the near future. Epic then posted an official teaser image along with a link to a YouTube livestream for the official announcement that began at 8 AM ET.
Epic Games have revealed the Fortnite X Batman collaboration on the YouTube live stream. The collaboration includes a new POI on the Fortnite Battle Royale map, Gotham City, which takes it’s place where Titled Town used to be.

Welcome to Gotham City challenges and rewards are also part for the collaboration along with Batman themed cosmetics including skins in the Item Shop.
The Catwoman skin is now available to purchase in the Fortnite Item Shop along with other Batman themed cosmetics:

The Welcome to Gotham City challenges and rewards are now live along with the rewards. We’ll be posting guides for the challenges shortly.