Emmerdale pub owner Charity Dingle (played by Emma Atkins) split up with Mackenzie Boyd (Lawrence Robb) after finding out he cheated on her with Chloe Harris (Jessie Elland).
However, their one-night stand resulted in an unexpected pregnancy, and Chloe soon gave birth to baby Reuben.
The young mum has told Mack that he is the father, however, fans are not so convinced.
During Friday's instalment, Mack and Chloe went to the registry office to sort Reuben's birth certificate.
They decided Reuben would take Chloe's surname Harris, but that his middle name would be Boyd.
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Fans have since come up with their own wild theories about Reuben's real father, and one even suggested Mack may kidnap the newborn baby.
Taking to Twitter. @GeorgiaBowring #Emmerdale shared: "Mack will kidnap the baby!"
@Katie_Murphy776 tweeted: "Oh, well since they're going to put his name on the birth certificate - then it's not Mack's kid. plot twist incoming."
Others suggested Nate is the father of baby Reuben, with @PaulPoeUK theorising: "It’s going to all kick off when it turns out the father of Chloe’s baby is Nate. #Emmerdale."
@MickJohnPNEFC went on to predict: "Nate's the dad #emmerdale."
@EnfieldGarry tweeted: "Ooh Nate’s getting it now. #Emmerdale."
As Chloe and Mack walked into the cafe together with baby Reuben, Charity looked heartbroken.
As Chloe made here excuses to leave, Mack confessed they had been to the registry office.
"It's not a big deal but we put my name on the birth certificate," Mack explained.
"Not for my sake but for Reuben's, so he has got a dad on there as well as a mum."
As Charity asked to see the birth certificate, she said: "His surname I am just curious."
"Harris, it is Harris... Reuben Boyd Harris," Mack replied.
Emmerdale airs weekdays at 7.30pm on ITV.
