Big Brother 27,' hosted by Julie Chen Moonves, premieres on Thursday,. See which houseguests are in power as HoH, who is nominated and who has been evicted so far

Before the season 27 premiere, many fans speculated that the mystery houseguest could be anyone from Celebrity Big Brother UK star JoJo Siwa to a Big Brother newcomer like Tom Sandoval from Vanderpump Rules. Viewers even hypothesized that this season, the host herself, Julie Chen Moonves, would join the cast as a contestant.

"Big Brother" is set to premiere this week. For Season 27 of the hit reality competition series, the official theme will be "Big Brother: A Summer of Mystery," CBS confirmed Wednesday, July 2.

Everything you need to know about ‘Big Brother’ season 27, including how to watch, where to stream the live feeds, and the cast.

Sleeper car bunk room: Behind a secret entrance, this train-themed bedroom straight out of a murder mystery novel contains bunkbeds for six Houseguests (the first time the BB house has had bunk beds since season one!) and a sleek Art Deco design.

"That's a world I don't even want to imagine," Chen Moonves responds when asked about a 'Big Brother' future without her