Her revelation comes next Monday (February 18) when Gail (Helen Worth) will find out that Lewis blackmailed Kylie into giving him her bank details.
Speaking to the Radio Times, Kylie actress Paula Lane teased: "There are three scenes where Gail is literally ready to pounce. She just wants to ask Kylie why she's done this after everything she's done for her.
"Kylie tries to wriggle out of it and makes a story up on the spot, but it's really quite hairy at this point! She's doing anything she can to divert Gail and throw her off the scent."
Of the aftermath of Kylie's admission, Lane said: "She goes straight for Gail's soft spot. Kylie asks Gail to allow her to explain for David's sake because she knows that Gail's priorities lie with her children.
"It prevents Gail from taking it any further, but when they finally sit down Kylie does have to admit that she slept with someone else. And Gail's then horrified that the baby might not be David's - she can't believe that she's done this to her son.
"[Kylie]'s massively worried and she goes into complete meltdown! She thinks that as soon as David comes back from his course that will be it."
The pregnant Bistro worker then goes to the Rovers Return where she ends up in a precarious situation on a table while drunk.
Explaining the incident, Lane added: "Kylie's in a really strange mindset when she goes into the Rovers and it's almost as if she's deleted everything that matters to her from her memory. She pretends she's not pregnant and gets drunk because the consequences don't matter at that point.
"When Stella tries to grab her Kylie stumbles and ends up banging her side really severely on a stool and falling to the floor. She's then rushed to hospital where she's told that the baby might not survive. She's devastated and she feels really embarrassed and ashamed."
Digital Spy Soap Scoop video - watch Amie Parker-Williams reveal the biggest storylines coming up in EastEnders, Coronation Street, Emmerdale and Hollyoaks next week: