Big Brother 27 mystery houseguest Rachel Reilly is married to Brendon Villegas. They have two children - daughter Adora Borealis Villegas and son Adler Mateo.

The most popular pick, handsdown, of who the mystery guest is would be none other than Rachel Reilly. She already made two appearances on the reality show, and won season 13, but she could be back for more. What gave it away for fans was a license plate that had the dates of July 2011.

Big Brother 27’s mystery 17th houseguest has entered the house, stunning the cast. Host Julie Chen Moonves revealed her own surprise at the selection to Entertainment Weekly:

Big Brother has unveiled a new cast of scheming players, and teased the mysterious returning alum. We have a theory!

The new season of "Big Brother" kicks off July 10, airing on CBS. Here's when new episodes air, and who the new group of houseguests are.

Big Brother follows a group of people living together in a house outfitted with more than 100 cameras and 100 microphones, recording their every move 24 hours a day. Each week, someone will be voted out of the house, with the last remaining Houseguest receiving the grand prize of $750,000.