Epic has announced the 'Rift Tour' (opens in new tab) will take place in Fortnite from August 6 to 8, wherein players will "take a musical journey into magical new realities where Fortnite and a record-breaking superstar collide." According to both court documents and unofficial leaks (opens in new tab), the performer on this occasion is Ariana Grande, with Lady Gaga booked in for a series of shows in December.
The Rift Tour's schedule suggests it'll be consistent with last year's series of Travis Scott concerts (opens in new tab), which were big in several ways: Scott appeared as a towering behemoth during the event, and the shows attracted a record concurrent player count for Fortnite of 12.3 million (it was also a big score for Scott, who reportedly earned roughly $20 million from the event (opens in new tab)). Marshmello (opens in new tab) has also performed in the past
There are a bunch of challenges already live in-game building up to the event which reward players with various cosmetics, and a temporary in-game tab for the five events that will take place over the three days. Epic will be announcing more on August 2, which I'm sure will be grand.