She was told by pals that ex-footballer Jermaine, 40, had taken the adult entertainer to his hotel room on a wild stag do in Ibiza.
A source said former reality star Jess, 34, was “heartbroken”.
The flame-haired dominatrix -booked through event planners Chillisauce - had put on an S&M performance for the stags before partying with the group at the Spanish isle’s Eden nightclub.
Sources claimed that Jermaine was “the last man standing” and alleged he took her back to the hotel room he was sharing with another member of the party.
Jess attempted to move on from the incident in May - at a time she was undergoing IVF treatment to start a family with Jermaine.
But recently she learned Pennant - who has admitted to cheating on multiple partners in the past - had been sending flirty messages to other women.