The Albert Square legend's character Phil Mitchell is paid a shock visit by ex Sharon Watts later this month (August 13).
> EastEnders Letitia Dean as Sharon Watts - Soap Icon
Hinting that Shirley will soon break up with Phil, McFadden told MSN: "It was a bit of a roller coaster really. One minute I'm up on the roof with Shirley, the next thing Sharon comes bursting through the doors and I'm sorting out her problems.
"Then Shirley makes a discovery and their relationship starts to unravel. So yeah, it's a roller coaster really."
Sharon's return to Walford will coincide with the revelation that Phil's son Ben murdered Heather Trott.
> EastEnders Sharon return scenes - more unseen pictures
The 53-year-old added that reuniting with Dean reminded him of "the old days", saying: "I hoped Letitia was looking forward to coming back, and that she was just how she was before she left.
"And that's exactly what I got. She was really happy to be back and it was just like the old days really."
"Sharon is an iconic character, she's one of the greatest characters on the show in the last 27 years," he said.
"Everyone's really excited about her coming back. She brings a weight of history back with her - a living history behind her. Letitia is a great actor and great to work with."
> EastEnders Sharon return will be brilliant, says Steve McFadden
Watch the EastEnders trailer for Sharon's return below: