Season 4 brought a new feature to Fortnite Battle Royale, Blockbuster Challenges. Players are required to complete all challenges for the week to complete the Blockbuster Challenge, unlocking a loading screen, which contains a clue as to where a hidden Battle Star can be found on the map.
Here is the Blockbuster loading screen for Week 5:
Looking closely at the loading screen, you can see the Battle Star in the background:
Here is the exact location for the free hidden star, thanks to SquatingDog:
Here’s a full cheat sheet map for Fortnite Season 4, Week 5: