Fortnite is the Battle Royale game that has taken the world by storm in the last few months - it's free, it's on almost every platform, and it's seemingly being played by everyone, wherever you look. But how much does it owe to other games, such as PubG? And is it here to stay? Julia Hardy and Steffan Powell have been finding out - with help from Twitch streamers, including Dr Lupo, a streamer who regularly draws in millions of viewers.