"Big Brother" Season 27 contestants better grab a life vest, because star Rachel Reilly is checking in as the 17th houseguest

In Season 27 of "Big Brother," houseguests will spend the summer inside Hotel Mystère, an enigmatic yet luxurious version of the "Big Brother" house.

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

Rachel Reilly is back in the Big Brother house, and fans are either cheering or ready to change the channel. The Season 13 champ made a surprise entrance on the July 10 premiere of Big Brother 27 as the long-rumored “mystery houseguest,” after CBS teased her return with a week of cryptic clues.

Big Brother fans are buzzing about the show’s latest twist, and they think they’ve got it uncovered. During the Season 27 premiere on July 10, the mystery 17th houseguest, Big Brother legend Rachel Reilly, was revealed. But that wasn’t the only surprise in store for fans for this season's "Summer of Mystery."

"So there's going to be a strong reaction in both directions for this mystery Houseguest."Ahead of season 27, here are the 12 best Big Brother seasons to watch, all of which are available to stream on Paramount+.

Grab a life vest, floaters, because look who just resurfaced back in the Big Brother house.

Rachel Reilly and Brendon Villegas met on 'Big Brother 12' and built a lasting marriage after winning fans with their showmance

‘Big Brother’ Host Shades the ‘Bachelor’ Franchise’s Failed Romances originally appeared on Parade. Julie Chen Moonves believes Big Brother is better at producing lasting love stories than the Bachelor franchise.

Big Brother 27 kicks off with Julie Chen Moonves' dramatic abduction, Vince grabs the first HOH title, and Rachel Reilly returns as a surprise houseguest.