Past housemates and celebrities including - Lauren Harries, Alex Reid, Sophie Anderton and Reveal's TV columnist Nicola McLean - headed to Elstree Studios in Hertfordshire on Thursday (26 September).
Stars gathered to celebrate the National Trust's London Project, which will give members of the public the opportunity to see inside the house for the very first time.
Other guests such as Brian Belo and Nikki Grahame also made an appearance, but they returned to a very different house from when they both appeared on the show almost seven years ago!
Guests scoured every area of the famous house including the bedroom, luxury room, treehouse and the Diary Room, all while sipping on BB themed cocktails - Sparkling Eviction and Trust Tease.
Big Brother's 'voice' also summoned guests to gather in the living room for a panel discussion. Big Brother series 14 housemate, Dan Neal, said: "Big Brother is such a big thing and through social media the fans get to interact with us more. The house is a national treasure."
Meanwhile, twins Jack and Joe Glenny added: "It's something you grow up with and watch, and it's a good thing for people to see the environment that we lived in."
Guests were also treated to a backstage tour of the camera set, observing all the house activity from a distance, as well as rifling through drawers of housemates' costumes from this year's tasks. And by the end of the night, everyone was well and truly evicted!
Now, for two days only, the house will open to 500 members of the public who bought tickets to have a tour of the iconic house.