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

In announcing the “Summer of Mystery” theme, CBS teased that Big Brother 27 would introduce a surprise “Mystery Houseguest” as a 17th player this season. Throughout the week, the Big Brother Instagram account has sent a variety of cryptic clues through various photos of the house.

Rachel Reilly, winner of Big Brother 13, was unveiled as the "mystery houseguest" competing again this summer on season 27.CBS had been teasing a secret player all week and dropping clues on social media as to who it was.