The actress looked stunning in a one shoulder black dress and designer heels, reported Daily Mail.
The Oscar-winning star separated from her director husband Sam Mendes in March this year after a marriage of seven years. At that time the couple stated the "split is entirely amicable and is by mutual agreement."
She has two children - daughter Mia, 9, from her first marriage to Jim Threapleton and 6-year-old Joe with Mendes.The 'Titanic' star has been pictured with her new boyfriend on several occasions but it is their first red carpet appearance.
The actress started dating the model only a few months back but is said to be smitten by him. The couple have been inseparable all summer and she apparently doesn't want the relationship to hit a stumbling block when she travels to make her next movie in Chicago.
She's committed to film 'Contagion' for several months and friends say the actress wants her new man to keep her company there.
"Kate hates the idea of having a long-distance relationship, even for a short period of time. They are absolutely smitten. They loathe being apart and so are taking their romance to the next level," a source close to the star said.
"Kate has been relatively free of work commitments since her split with Sam so she and Louis have managed to enjoy lots of time together. But that is all about to change as she gets her teeth into this next movie and she will be spending a lot of time away from home," the source said.
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