The Oscar-winning actress looked stunning in a floor-length midnight blue gown at a screening of Labor Day at the Toronto International Film Festival on Saturday (7 September).
Kate plays a single mum who is forced to take in a convict in the movie, and she told reporters at a press conference earlier in the day that she used her own experience of motherhood when preparing for the role.
"I have admiration for mothers everywhere, whether they're single or not – and for fathers, too. It turns you inside out," she said.
According to Entertainment Weekly, although Kate walked the red carpet at the premiere, she skipped the screening, explaining earlier in the day that watching the movie would be "weird" because of a particular plot line about childbirth.
Kate is expecting her first child with husband Ned Rocknroll this year. She is already mum to 12-year-old Mia, her daughter with first husband Jim Threapleton, and 9-year-old Joe, her son with second husband Sam Mendes.
The Titanic actress confirmed her third pregnancy in June, with a rep saying the couple are "thrilled" to be expanding their family.
She married Ned, the nephew of Sir Richard Branson, in a private ceremony in December 2012 following a summer engagement.
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