Jennifer, 28, looked amazing at the premiere in a black gown while she accessorized with a silver necklace and showed off her beautiful diamond ring.
"Well, he's just the best person I've ever met in my whole life," the A-lister told ET of Cooke, 34 at the film's debut.
"It was a very, very easy decision," she added with a smile.
As OK! readers know, the couple had been dating for eight months before Jennifer confirmed her engagement in February.
The Hunger Games alum gave her fans a glimpse of her new rock at the Paris Fashion Week Christian Dior show. The ring is reportedly four to five carats and worth around $200,000.
On May 12, the pair celebrated their love at an intimate engagement party that Jennifer hosted in New York City.
What do you think of think of Jennifer's comments regarding her engagement? Let us know in the comments below!