Emmerdale aired a huge betrayal on Thursday, as Mackenzie Boyd cheated on Charity Dingle with a mystery woman.
Towards the end of the episode he was seen in bed with the unknown person, with only her arm and hand shown to viewers.
But fans believe they have cracked the case and know who Mackenzie slept with, ahead of his betrayal causing drama for him in upcoming scenes.
The couple spent the day at a wellness retreat, with Mack using the opportunity to open up about his feelings.
They recently lost their baby after Charity suffered from an ectopic pregnancy, leaving them both devastated.
Since then, Mack has repeatedly told Charity that he wants to try for a baby again, while Charity has said she is not keen, already being a mother to four.
The differing hopes for the future have come between them, and Mack decided the retreat might help bring them closer again.
Things didn't go well though when he shared his hopes to talk properly with her, and to start a family with her in the future.
As Charity told him it wasn't what she wanted and that she might not fall pregnant again, Mack didn't listen and instead suggested they looked into IVF.
Charity lost it, and told Mack: "If you wanna be a dad some day it is not gonna be with me, so if you are that desperate to have a sprog you are gonna have to find somebody else."
As things got heated Mack stormed off, leaving their romance on the rocks.
But after a chat with Mack's sister Moira, Charity realised she may have been a bit harsh with her remarks and didn't want to completely rule out having a family with her partner.
She decided to speak properly with him about everything, but he wasn't at home and was not answering his phone.
As Charity grew worried, she apologised for her comments and begged him to reach out to her, telling him she loved him in a voicemail message.
What she didn't know though was that Mack was in bed with another woman in a hotel room, and he didn't seem to have any regrets.
As he checked his phone and saw the missed calls from Charity, he smirked when the mystery woman knocked his phone out of his hand, before the pair got steamy again.
While the unknown female was not shown on camera in full, viewers did see her arm and her hand and they believe they were able to work out her identity.
Taking to Twitter, viewers shared their theories and many were convinced that it was none other than Chloe Harris who made a reappearance in the same episode, having been "missing" for a while.
One fan wrote: "God knows who Mac has copped off with. Probably Chloe as we actually saw her face tonight. It better not be Belle after she’s JUST told Chas how awful cheating is."
Another predicted: "Won't be the Belle the lecture she's given Chas for cheating. My bet Chloe," as a third added: "My guess is Belle or Chloe with idiot Mack."
A fourth fan tweeted: "That Chloe girl has been with everyone, so maybe her?" as another said: "Mack with Chloe? She's done everyone else, not judging after all its not my business, but am just saying."
Meanwhile another viewer pointed out: "Don’t think that was a ‘random’, as they would’ve shown their face…"
Emmerdale airs weeknights at 7:30pm on ITV, with an hour-long episode on Thursdays.
