Rocking slicked back hair, Alexander stunned in a red, purple, green, blue and black sequined Armani Prive dress. The 31-year-old Blindspot actress kept her jewelry to a minimum, with simple jeweled earrings to complement her huge diamond engagement ring. Her beau, 41, kept it classy in a black suit and bowtie.
Facinelli popped the question to Alexander in March atop the Empire State Building, after nearly three years of dating. They met while co-starring on the Showtime series Nurse Jackie.
ET caught up with Alexander on the carpet. When asked when the wedding will be, her response was precious.
"Oh you know, I actually don't know," she said. "I don't have time to plan that right now but eventually. Who knows, maybe we'll just go to City Hall. Make it easy!"
This will be the first marriage for Alexander, and second for her fiancé. Facinelli was previously married to actress Jennie Garth. They were together from 2001 to 2013 and have three kids together -- Luca Bella, Lola Ray and Fiona Eve.
Garth recently tied the knot with actor David Abrams in July. Watch the video below to see gorgeous photos from their tear-filled ceremony!