What happened on 'Big Brother'? Who is the mystery houseguest? Season premiere recap

"Big Brother" is back, as the long-running CBS show launched its 27th season July 10.

But what happened during the premiere episode? And did viewers learn the identity of the mystery houseguest?

Here's everything to know from premiere night.

What happened on the 'Big Brother' season 27 premiere?

To open the night, Julie Chen Moonves introduced the first eight houseguests:

Kelley Jorgensen.

Zach Cornell.

Ashley Hollis.

Rylie Jeffries.

Amy Bingham.

Adrian Rocha.

Lauren Domingue.

Keanu Soto.

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Zach, Amy, Adrian and Kelley were the first four to enter the house, with Zach being the very first houseguest to walk through the doors (super fans know that's a big deal).

In the diary room, Kelley complained about Amy being too loud off the jump, before cameras showed a countdown clock.

Morgan Pope, from left, Adrian Rocha and Ava Pearl reacting to the mystery houseguest.

The other four then entered the house.

Julie then introduced the second eight houseguests:

Katherine Woodman.

Vince Panaro.

Mickey Lee.

Jimmy Heagerty.

Morgan Pope.

Isaiah “Zae” Frederich.

Cliffton "Will" Williams.

Ava Pearl.

Mickey, Zae, Katherine and Jimmy entered the house. Jimmy quickly said he and Amy had a connection.

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Julie then told the last four to go into the house.

Mickey, in the diary room, mentioned she saw some attractive men in the house, and specifically named Rylie. Zae and Keanu also mentioned having a bro connection.

Julie ultimately came on the TV and talked to the houseguests, but the countdown clock hit 00:00 and the lights went out. Once the lights came back. Julie had disappeared from the stage and left a single high heel.

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 disappearances of Julie and the HOH relic. Julie called the houseguests on a phone and told them that eight people would try to find her and the other eight would look for the HOH relic.

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Amy, Zach, Ava, Vince, Adrian, Mickey, Lauren and Rylie competed in a competition with the end goal being to save Julie. Zach ultimately won, and Julie popped out of a door.

Kelley, Will, Jimmy, Ashley, Morgan, Zae, Katherine and Keanu competed in a second comp to find the HOH relic. Jimmy came out victorious.

Julie, back out in her normal spot on the stage, later told the houseguests that Zach won $10,000 for finding Julie. Jimmy, on the other hand, could pick the four houseguests that would compete in the Head of Household competition, as only four participated.

Jimmy talked to his fellow houseguests, and many didn't want to compete in the first HOH comp. Ultimately, he chose himself, Adrian, Ashley and Vince.

Zach Cornell and Vince Panaro during the "Big Brother" premiere.

Vince won the first HOH of the season.

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Julie then said something about the mastermind's lair exploding, and, before commercial break, the show naturally flashed a fake shot of a lair exploding out in the wilderness.

Once back in the living room, Julie told the houseguests that the AI Arena would return this season, with a new name: the BB Blockbuster.

The odd mastermind guy then cut back onto the screen and revealed the mystery houseguest: "Big Brother" legend Rachel Reilly. After everyone reacted to Rachel coming into the house, the mastermind revealed that one of the original 16 houseguests was his accomplice. If they can't figure out the person's identity, then they will stay in the game and 17 houseguests will compete this summer.

Who is the mystery houseguest on 'Big Brother'?

"Big Brother" legend Rachel Reilly, who won season 13, is the mystery houseguest. She said she is staying in the house.

Who won HOH on 'Big Brother'?

Vince Panaro won the first HOH.

Vince Panaro is a houseguest on this season of "Big Brother."

What days will 'Big Brother' air this year?

In addition to hour-long episodes Sundays and Thursdays, "Big Brother" will also have 90-minute episodes on Wednesdays, airing from 8-9:30 p.m. ET.

Julie Chen-Moonves in the "Big Brother" season 27 house.

It will also add "Big Brother: Unlocked" every other Friday, starting July 25, from 8-9 p.m. ET. The show will feature "three BB All-Stars (who) offer never-before-seen broadcast footage from the house, exclusive interviews, surprise guest appearances and unprecedented behind-the-scenes access. Former Houseguests (will) share firsthand insight and expertise as they analyze gameplay, assess the competition and give their insider’s perspective," according to a press release.

Who is on the 'Big Brother 27' cast?

CLICK HERE to read more on this year's houseguests.

When do 'Big Brother' live feeds start?

According to Parade magazine's Sharon Tharp, live feeds start at 12:30 a.m. ET July 14.

Will 'Big Brother' live feeds have the flash back feature this year?

While the answer to this question has been unconfirmed, Parade magazine's Mike Bloom reports that the feature won't return after being removed last season.

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'Big Brother 27' house

How many seasons of 'Big Brother' are there?

Technically, there are 26 seasons of "Big Brother." But there have been three seasons of "Celebrity Big Brother," which Chen Moonves toldUs Weeklyshe expects to return during an upcoming winter.

There was also one season of the spinoff series "Big Brother: Over the Top," and the"Big Brother Reindeer Games" holiday specialaired for the first time in 2023.

"Big Brother" season 27 starts July 10.

This article originally appeared on Cincinnati Enquirer: What happened on 'Big Brother'? Who is mystery houseguest? Quick recap