The actress's character Heather Trott excitedly agrees to marry boyfriend Andrew (Ricky Grover) when he pops the question unexpectedly next week - but her best friend Shirley (Linda Henry) may take longer to warm to him.
In an interview with Inside Soap, Fergison admitted that Heather is taking a risk by making a commitment to Andrew as he has already shown a darker side.
"Heather has put her trust in Andrew in a very short space of time. Recently she walked into the café to see Andrew turn over a table in anger, so she knows he has a temper," Fergison explained.
"But Heather really wants things to work out. She's aware there are alarm bells ringing, and whereas in the past she would have totally ignored them, she's more wary these days. But when better things override that and he's her lovely Andrew again, it's all fine."
Revealing Shirley's take on the situation, she continued: "There has always been friction between Shirley and whichever man Heather gets involved with. I think she was even jealous of baby George when he was born.
"That means there'll be serious sparks as the friction between Andrew and Shirley grows. We're talking fire and brimstone! And that's going to bring out this other side of Andrew once more."
EastEnders fans will see Heather depart the show in a few weeks' time - as announced by bosses last year.
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Watch Heather's EastEnders character trail below: