Big Brother season 27 premiered on July 10 with a 90-minute episode. During the premiere, season 13 winner Rachel Reilly was unmasked as the "mystery Houseguest" who would be joining the contestants in Hotel Mystère. In July 2025, Chen Moonves told Entertainment Weekly that "people should be afraid of [Reilly] and of getting in her crosshairs."

These 16 houseguests and one reality television legend moved into the famous “Big Brother” house for a summer filled with competitions, alliances and back stabbing.