According to The Sun, the grief-stricken character will turn to Rainie (Tanya Franks) for comfort amid his devastation over wife Ronnie's dramatic baby swap confessions.
While Ronnie spends time in jail for her crime, Rainie apparently gives Jack (Scott Maslen) a shoulder to cry on, which soon leads to them spending the night together.
A source told the newspaper: "Jack's a real mess. He's lost his son and his wife. Rainie is there for him."
Fans had speculated that the plot twist was ahead as the official synopsis for a forthcoming episode states that "Jack finds himself being comforted by Rainie as he continues on his path of self-destruction". However, further details had not emerged until now.
Rainie returned to Albert Square for her sister Tanya's wedding earlier this month. Her last stint on the show in late 2010 saw her contribute towards Phil Mitchell's crack cocaine addiction as she was present throughout his downward spiral.
Jack and Rainie's scenes are expected to air early next month.
> Read our EastEnders spoilers and news