The pair took just two days to end up snogging after Sam joined the house on Thursday night.
Sam and Ellie, who have both appeared on ITV2 reality show Ibiza Weekender, enjoyed a cheeky kiss on the floor of the kitchen.
It followed Ellie warning Sam not to mess her around like former housemate Lotan Carter.
"I've not come in here for you because I didn't know you were in this show," Sam told Ellie.
She replied: "All I'm asking is don't f**k... do you know how many people have said I've been messed on this show by Lotan, it's been pretty obvious."
Sam reassured her: "I'm not going to mess you around, I'm not that type of person."
After their snog, Sam told Ellie: "Don't tell anyone, don't say anything."
The couple's kiss comes despite Deborah warning Ellie that Sam could be playing a game.
She told Ellie in the house yesterday: "Aren't you super paranoid he has his own agenda coming here?
"I know people have watched this show probably before coming so he could be close to you because he knows you're doing well on the outside."
And viewers were quick to agree, with one tweeting about Ellie and Sam's kiss: "Game player if I've ever seen one"
Another posted: "Watch out Ellie he's just using you ☹️"
Big Brother 2017 continues nightly on Channel 5.