Emmerdale fans know Mack's lover is a married woman - as he continued to feel guilty over the affair.
Fans of the ITV soap have been speculating for days over who the lover might be, with many names including Chloe, Belle, and even Aaron Dingle being thrown into the ring. Mack is set to be harassed by his secret lover, who we know is a local in the village.
He cheated on his girlfriend Charity Dingle after the pair sadly lost their child in an ectopic pregnancy. Devastated by what happened, Mack decided to seek solace in someone else and whilst the affair is long over, his guilt still stands.
During tonight's episode of the ITV soap, Charity and Mack bumped into Nate in the café, and then was an awkward exchange, as Nate desperately tried to reassure Charity Mack was really focused on her - despite her not even knowing about the affair.
Later, as the pair sat down on the sofa after dinner, Charity seemed confused by what happened earlier, as she remarked to her boyfriend: "Hey, by the way, you know earlier when we were in the café, Nate seemed a bit weird - like a lot weird."
"Let's be honest, he is a mate but he's a lot weird," Mack hit back, clearly trying to avoid the conversation.
However, Charity continued to discuss it, admitting she was puzzled by Nate's weird behaviour.
"Just some of the stuff he was coming out with was weird; it was like he was on the defensive or something. Like he had something to hide," she mused as Mack said the news about Nate's girlfriend Naomi being one of Nicola's attackers probably didn't help.
He replied: "Well he's just found out his girlfriend's a lunatic. Like a proper psycho so his mind will have been all over the place," as Charity then told him: "I know guilt when I see it and it was like it was written all over his face."
After their exchange, fans are now sure they know who he slept with - and the theory shocked us too.
"Ok, then my money's on Marlon's wife!" one fan suggested, as another replied: "Yeah Mack and Moira are brother and sister! Oooh you might be onto something there though, Rhona is a good shout!"
A third guessed: "I meant maybe it's rhona who slept with mack . She's bored with marlon already."
*Emmerdale airs weekdays on ITV at 7.30pm.
