The American Sniper star split from the actor last year (15) after four years together, and made a fresh start in August (16) by moving across the Atlantic to New York with their daughter Marlowe, four.

She has now revealed in an interview with The Telegraph magazine that Tom relocated with them and they are living together as a family, although they are no longer romantically involved.

"It's cool. It works," she said. "I know, it's very modern. We do everything together and I'm very lucky to have managed to retain that. Genuinely."

They are currently living in a spacious brownstone in the West Village which is totally "unsustainable" as she can't afford to stay there permanently.

"I can do it for about six months and then it's downhill...," she joked. "I felt like I'd uprooted everyone, so I said, 'Let's just chuck money at it.' And now the reality is Marlowe's loving it, Tom's loving it..."

She had been considering a move Stateside for a while but finally made the decision when she realised she would have to travel to America to promote her upcoming movies Live by Night and The Lost City of Z next year (17) and didn't want to constantly uproot Marlowe.

Sienna, 34, is planning to stay for "at least a year" but there are already aspects of England that she misses, such as "my friends, nice pubs, the countryside." However, they are returning to the U.K. for Christmas, which she is hosting with her family.

"This year I really want to be organised. I'm that person on Christmas Eve crying in (department store) Selfridges because I'm panic buying," she laughed. "It will be pyjamas and too much booze and a few fights. We always aspire to be elegant but don't really get there."