Gregg DeGuire / WireImage 1 / 7
Gregg DeGuire / WireImage 1 / 7

Alexis Bledel's red-carpet wardrobe just got even better! The 31-year-old actress attended the L.A. premiere of her TV movie "Remembering Sunday," on Wednesday, bejeweled with her sizable new engagement ring from "Mad Men" co-star Vincent Kartheiser -- and it's a beauty.

PHOTOS: Co-star couples

Bledel looked stunning in a black and white Pamela Roland cut-out dress, but all the focus was on her ring finger. The gorgeous ring features a massive, round-cut diamond on a simple platinum band.

"Vincent picked it out," the "Gilmore Girls" alumna gushed to Us Weekly on the carpet. After nearly a year of dating, Kartheiser, 33, popped the question last month.

PHOTOS: Best celebrity engagement rings of all time

Bledel, who guest-starred on Season 5 of the AMC smash as the mentally unstable mistress of Kartheiser's character, Pete Campbell, said she'll be getting help from her future husband when it comes to planning their wedding.

"We're doing it together," she told Us. "We haven't started yet though."

VIDEO: What to wear to any type of summer wedding

When Us chatted with Kartheiser at the Season 6 premiere of Mad Men on March 20, the groom-to-be was still adjusting to the engagement. "I keep saying girlfriend," he said. "And then I'm like, 'I mean, my fiancee!'"

But the actor added, "I'm a very lucky man."


Most expensive celeb engagement rings

Kim Kardashian's tightest looks

Best off-season bikini bods