Max (Jake Wood) is currently one of three men left in the frame in Kat Moon's affair mystery, which has been running since July.
The Walford businessman is currently planning to marry his partner Tanya again, but his history of infidelity means that he remains a likely suspect.
Jossa told the Daily Star: "If Max is Kat's secret boyfriend then Lauren will be fuming. I can promise you she'll kick off big time.
"I think it would be the last straw for her and Max. She would think Tanya is a nutter if she got back with him again."
Max's brothers Derek and Jack are the two other men still under suspicion, after Ray Dixon and Michael Moon were officially ruled out.
Next week's episodes see the mystery guy in question continue to pursue Kat after she returns from holiday, but fans will have to wait and see whether she succumbs to temptation or not.
Photo gallery - Kat Moon affair suspects: