Leighton - who met Adam on the set of indie film The Oranges in 2011 - stunned in a sleek Emporio Armani metallic blue shift dress complete with a ribbed skirt and accessorised with nude heels and a satin clutch, both by Armani while she walked the crimson carpet.
But the outfit was soon forgotten as we caught sight of her sparkler.
"Set in a rub over setting, Leighton's diamond looks to be approximately 3.5 carat. Similar to her Gossip Girl co-star, Blake Lively, Leighton's ring is also rose gold - a growing trend across the celebrity world."
Us mere mortals at can only dream of an engagement ring so beautiful... And a husband at dreamy at
Seth Cohen Adam Brody. Siiiigh.
Check out how Leighton's rock measures up to these other celebrity engagement rings in the gallery below.
MORE! Adam Brody confirms he tied the knot with Leighton Meester but delivers the news in the most non-celeb like manner possible...