And clearly, the 27-year-old star wanted to get noticed. This lace and feather Monique Lhuillier gown is what you call a head-turner.
Paired with a sparkly fish-shaped clutch bag by Judith Leiber, diamond earrings and side-swept curls, Blake embraced vintage Hollywood glamour for the event.
As her husband Ryan Reynolds was away filming Deadpool in Canada, she was joined by her mother Elaine and brother Eric at the premiere - but the ravishing red look didn't last for long.
The former Gossip Girl actress made a quick change into a sheer bodysuit and black coat, also by American designer Lhuillier, for the after-party held at NYC's Metropolitan Club.
You'd never guess Blake gave birth to her daughter, James, just four months ago. The actress welcomed her first child with Reynolds near their home in Bedford, New York in December 2014.
Love Blake's look? See more stunning red carpet style below:
So that's her secret...
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