As series four begins Robert finds himself facing what Hugh Bonneville calls, “A double calamity,” with the breaking of his daughter Mary’s heart and the loss of Matthew, his heir.

Here’s what Hugh had to say about the new series and the challenges that everyone at Downton – but especially Lord Grantham – are set to face…

He said, “The family is traumatised and Robert’s responsibility is to protect his daughter as best he can from the agony she’s going through.”

But alongside this, he of course has to protect Downton itself, and this is going to prove to be difficult with potentially catastrophic death duties looming large.

Hugh explained, “At the beginning of the third series, we saw Robert’s own folly jeopardising the future of the estate.

“This time, it’s something he could not have avoided, which is the death of his heir and the burden of death duties.

“50% of the estate was owned by Matthew, and punitive taxes are now due to the revenue.

“What is he to do? How can he best preserve Downton for his new heir, the baby George?

“Robert’s aim – as it has always been – is to try and do the best for the estate and for the family.”

What Robert thinks is best for his daughter Mary is that he protect her from the outside world, but of that, Hugh said, “Unfortunately, this well-meaning approach may not actually be what’s best for the very person he’s trying to protect.

“It’s as if he wants to keep Mary swaddled in her widow’s weeds, [but] what others in the family believe is that she needs to break out of what you might call the chrysalis of mourning.

“In the first episode, we see Robert almost suffocating Mary with his desire to protect her, out of fear of her going under.

“It’s somewhat overbearing and unhealthy, to be honest, but as she emerges from the darkness, so he delights in her new-found brightness of spirit as the story develops.”

And what of any potential suitors for his daughter?

Hugh said, “In terms of the other men around Mary, I think he longs for her to be happy. It’s as simple as that.

“She’s had more than her share of tragedy.”

There are, of course, not one but two grandchildren now in the house – Sybbie and George…

Of them, Hugh said, “I think Robert’s a doting grandfather. No question!”

However, things aren’t so cut and dried for Robert and his wife Lady Cora, but as Hugh explained, they’re still a solid partnership.

He said, “After the personal wobbles in series two, and then the devastation of what happened with Sybil, I feel that Robert and Cora are now closer than they’ve ever been.

“They’re united but they still have disagreements. For instance over his approach to Mary’s bereavement, but ultimately we feel that they’re on solid ground again.”

Bonneville then revealed that he’s looking forward to some major set pieces in episodes to come, and in particular, the party scenes.

He remarked, “I love it when we do the big ensemble scenes. I mean, they’re a nightmare to shoot – when you’ve got 15 or 20 people in one scene it’s always agony for the director.

“But the criss-crossing of storylines is always satisfying for the audience, particularly in scenes when the house is buzzing with activity.

“So I completely agree with Robert’s line, ‘It’s good to see the old house at full strength again.’

Yet though he says he loves the ensembles scenes, it’s the quieter moments that are Bonneville’s favourites.

He said, “The way that Julian writes Robert’s encounters with his daughters is really touching.

“There’s a beautiful one with Edith coming up which is very, very special.

“Robert cherishes the relationships with his children now they’re grown up. They’re independent young women who look to their father for wisdom and advice…

“But they often ignore it, probably rightly!”

As for the show’s phenomenal global success, Bonneville says it keeps the cast “on their toes.”

He explained, “It puts a notional pressure on us to keep the standards high, but then we were going to do that anyway for series four.

“And the opportunities the show’s success has afforded all of us are incredible and the invitations we’ve had from around the world are extraordinary.

“It won’t happen again in my lifetime so we’re all enjoying it while it lasts.”

Amen to that!