Published Thursday, 12 September 2013
Downton Abbey returns to UTV this month. (© ITV)
"The world in which Downton began has more or less ended and now they have to find a new way forward," he revealed.
"Immediately after the First World War there was a sort of dazed period where society - and I don't just mean high society - was trying to gauge how much had changed. We've done the third series, when people were almost tentatively trying to decide how different the world had become.
"The fourth (series) is more about getting into the 20s: what young people wanted, the changes in music, the arrival of the movies, cars, transport and all of that stuff.
"But also the difficulties of the big estates, with so many of them packing up."
The new series of Downton Abbey picks up six months after the tragic death of Matthew Crawley,
Viewers were shocked during last year's Christmas episode as moments after Lady Mary and her besotted husband Matthew rejoiced in the birth of their first child, a much longed for son and heir to Downton, a tragic crash robbed the newborn of his father.
Fellowes has said he thought very carefully about whether or not to move forward in time for the new series, and even then was not sure how far he should go.
"It seemed to be much more interesting to, if you like, jump forward to Mary beginning to reconstruct her life," he said.
"And by leaving it six months, we could start with her at her lowest ebb, but at the beginning of the period when it sort of becomes time for you to start getting out and about again, starting to make things happen once more."
Viewers will see Lady Mary not only deal with the loss of her husband, but also deal with advances from prospective suitors in the wake of Matthews death.
Julian explained: "I don't think in Mary's case it is believable that no man would have been interested: she's very good looking, she's clever, she's very well placed, she has a big estate; these women are pursued.
"The only reason she wouldn't be eventually courted successfully would be if she was determined to remain alone and I just don't think that's who she is.
"I think she's one of those people who find it quite difficult to be generally genial and those people need a partner, because otherwise there's no one they're ever completely relaxed with."
Downton Abbey returns to UTV on Sunday 22 September at 9pm.
© UTV News