Rachel Reilly, winner of Big Brother 13, was unveiled as the "mystery houseguest" competing again this summer on season 27.

A former 'Big Brother' player – and winner – was unveiled as the mystery 17th houseguest during the season 27 premiere.

Oh, summer hasn't officially arrived until "Big Brother" has arrived and it's here. The CBS reality competition series is celebrating 25 ...

After much anticipation, Big Brother Season 27 revealed the mystery houseguest. Former contestant and winner of the ...

Vince secures the first Head of Household title after a challenge win, while players are left guessing who among them is secretly working with the Mastermind.

The 27th season of Big Brother kicks off with a wild premiere that finally reveals who the "Mystery Houseguest" is before ...

"Big Brother" revealed its mystery houseguest for season 27 Thursday: the legendary Rachel Reilly. Reilly entered the house ...

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 ...

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

The long-running reality competition series "Big Brother" officially returns on Thursday, July 10 at 8 p.m. ET on CBS.

The first cheesy segment of the season then occurred: An odd man in a red mask appeared on the TV and said he was behind the ...