Her character Lady Mary Crawley is mourning the tragic loss of her husband Matthew and finds it difficult to bond with their baby. Michelle says she had to resist giving the twins lots of cuddles when the cameras were rolling.
"Mary is not as affectionate as I would be with a baby and I found it really hard," reveals Essex-born Michelle. "I want to cuddle them, but Mary’s practical and that’s the sort of mother she’ll be."
The name George was chosen, apparently as a tribute to George V, months before Prince William and Kate Middleton announced the same name for their first-born child.
Michelle reveals that Mary does become more maternal as the series develops.
"She definitely warms and bonds with the baby much more," she says. "In the beginning, he just reminds her of Matthew every time she looks at him."
Michelle admits that she misses Dan Stevens, whose character Matthew was killed in a car accident during last year’s Christmas episode. Dan decided to leave to pursue other roles.
Is she sad that she didn’t get to play at happy families on screen for longer? "I guess it wasn’t what I was expecting," she admits. "But as much as it was a concern to begin with, the writing has changed and it’s given Julian Fellowes (the show’s writer) an opportunity to take other characters into a different chapter."
Mary will attract the attention of three suitors during series four. She will be pursued by the dashing Lord Gillingham, played by Tom Cullen, jazz singer Jack Ross, played by Gary Carr, and the argumentative Charles Blake, played by former Foyle’s War actor Julian Ovenden.
She clashes with Charles at first, revealed Downton’s executive producer Gareth Neame."Blake is someone she just doesn't like," he said. "He's modern-thinking but does not share the family's sentimentality about the past."
In real life, Michelle is dating Irish PR executive John Dineen, who she met through her co-star Allen Leech.
The new series of Downton Abbey airs in the UK on 22 September at 9pm on ITV.