The actor, who plays Robert, Earl of Grantham in the hit period drama, described the upcoming episode as “very heartwarming” on The Graham Norton Show but refused to drop any spoilers.
“You’ll have a lump in your throat, but in a very nice way,” he said, suggesting that the show will be somewhat different to 2012’s special, in which Lady Mary’s husband Matthew was killed in a freak road accident the same day his son George was born.
“Isis is a very unfortunate name at the moment but it got a bit daft that people genuinely thought we’d reacted in some way to world events,” he said. “It shows a slight lack of understanding of how TV shows are made.
“Back in the nice days before we’d heard the acronym I mentioned to [creator] Julian Fellowes that the dog was getting on a bit and he said he would think about it.
“I’m not giving any spoilers, I’m just mentioning there is a storyline involving the dog that was a developed a year ago.”
Please let there be a puppy involved...
The Graham Norton Show airs tonight at 10.35pm on BBC One