https://www.pcgamer.com/fortnites-incoming-double-barrel-shotgun-sounds-like-a-double-pump-replacement/

The double barrel shotgun, a videogame classic since 1994, is coming to Fortnite Battle Royale. Evidence of the new weapon was dug up yesterday by XDA dataminers, and confirmed earlier today in the game. 

A two-shot boomstick is a common break-action shotgun in Fortnite: Save the World, but it hasn't made an appearance in Battle Royale yet. Details of the Battle Royale weapon, beyond what's in the tweet—"New Epic and Legendary shotgun that can be fired twice in rapid succession"—haven't been revealed, but based on that description it will be a rather more rare and valuable weapon than its StW counterpart.