Not only was the actress' outfit super sexy, it also gave the illusion of an hourglass figure, as it cinched in Jen's waist and accentuated her bust.
The gorgeous grey strapless dress was designed by British favourite Vivienne Westwood and featured plenty of layered fabric around the front, as well as a slightly asymmetric hemline.
Jen accessorised with a pair of nude heels and styled her blonde-brown hair simply, while drawing attention to her sparkling eyes with smoky make-up and lashings of mascara.
And clearly the 44-year-old film star adored her outfit, as she couldn't stop smiling for the evening.
Jen's noticeable glow and boost of confidence might also have been because fiancé Justin Theroux accompanied her to the famous film festival.
Proving to be the ever-supportive future-hubby, Justin was spotted on the red carpet with Jen and then heading inside for the premiere of her latest film, Life of Crime.
Earlier this year, the couple were rumoured to be expecting their first child together after the former Friends actress was apparently seen with a slight bump.
However, the speculation was quickly laughed off by Jen, who admitted that she had merely gained "a couple of pounds."
There is still no word on when the two lovebirds will be officially tying the knot.
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