The teenage reality TV star arrived at the showbiz event looking super sophisticated in a simple monochrome ensemble.
She teamed a cropped white T-shirt with a long black skirt that featured a thigh-high split and completed her outfit with a pair of strappy sandals.
Kylie, 16, also wore her dip-dyed brown hair down and sported a flawless face of make-up, with sweet pink lips.
Her best guy pal Jaden also attended Justin's premiere and turned up looking as eclectic as ever in a hoodie covered in letters of the alphabet, an extra long colourful T-shirt and a pair of shorts.
Jaden, 15, then kept things even more casual with a pair of statement sock and some Nike trainers. Well, at least the trainers matched!
Last month the Karate Kid actor and son of Will Smith was pictured wearing odd shoes on the red carpet alongside his sister Willow. So, by those standards, he actually appeared to be a little smarter this time around!
Also spotted in Los Angeles last night to show his support was R&B superstar and Justin's mentor Usher, who was dressed in cool, smart-casual attire.
But despite the large amount of famous faces and the impressive turn out, it was 19-year-old Justin who stole the spotlight. And rightly so!
The chart-topper attended his highly-anticipated documentary film premiere looking like the modern day version of Santa Claus in a red blazer, red jeans, a white shirt and white trainers.
He accessorised with a massive gold chain around his neck, an eye-catching gold watch and a pair of sunglasses and posed for photos with his posse of friends, as well as his mother, Pattie Mallette.
Aww - he's really just a mummy's boy under all that bling!
The Believe docu-flick follows the life of Justin during his sold-out 'Believe' world tour, which he embarked on this year - travelling to places including London, Ireland, China and Amsterdam - and it wrapped up at the beginning of December.
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