Twenty-four-year-old Blake was gorgeous in an illusion dress by Zuhair Murad.
The stunning gown, which perfectly accentuated her tiny waist, featured black linear detailing.
Giving her a distinct air of old Hollywood, her blonde hair tumbled in waves over her shoulder and her lips were scarlet red.
Blake often tops best-dressed lists, a feat made all the more impressive by the fact she doesn't employ a stylist.
"My assistant will call fashion houses for me, but I always pick the outfit, shoes, jewellery, and a lot of times I do my own hair and make up for events," she told Marie Claire.
"Sometimes I think, God, why do I do this to myself? It's so much extra work."
Blake said she looks after her own styling because she "loves fashion".
She added: "It's such an expression of self. I often see people and they look great, but I can identify who styled them. Every stylist has a signature.
"Maybe it sounds jerky, but I'm lucky to be on such a fashion-centric show," she said, referring to Gossip Girl.
"There's no designer I don't have access to."
Blake wasn't the only star looking stunning at the film unveiling this week.
Salma Hayek showed off her curves in a floor-length shimmering jade green column by Gucci.