The new parents made the announcement on Sunday. Teigen posted a screenshot of their little girl's birth weight -- 6 lb., 11 oz. -- along with the caption, "She's here! Luna Simone Stephens, we are so in love with you! And sleepy. Very sleepy."
The exciting news comes just one month after Kim Kardashian threw the Sports Illustrated model an untraditional baby shower at her home in Los Angeles, complete with a dessert table, McDonald's catering and customized Snapchat filters.
"My everything," she wrote. "Excited to meet this little girl soon and to see you shower her with the same love you give to me! We are so grateful to be surrounded by so many loving, kind, hilarious, generous, thoughtful beings. Feeling so lucky, so happy and so ready!"
A photo posted by chrissy teigen (@chrissyteigen) on
The two enjoyed a much more formal baby shower on March 6 in New York City with their closest friends and family. At the fancy fête, Teigen donned a bejewled "baby mama" crown emblazoned in glitter and guests enjoyed cookies shaped like baby carriages, bottles and onesies.
As ET previously reported, the new parents specifically chose their baby's gender when Teigen underwent in vitro fertilization last December, two months after they broke the news that they were expecting via Instagram. "I've made this decision," Teigen later told People. "Not only am I having a girl, but I picked the girl from her little embryo. I picked her and was like, 'Let's put in the girl.'"
"I think I was most excited and allured by the fact that John would be the best father to a little girl," she continued. "That excited me. It excited me to see ... just the thought of seeing him with a little girl. I think he deserves a little girl. I think he deserves that bond."
"As many of you know, we've been trying to have a baby for a while now," Teigen captioned an Instagram photo. "It hasn't been easy, but we kept trying because we can't wait to bring our first child into the world and grow our family."
"We're so excited that it's finally happening," she continued. "Thank you for all your love and well wishes. I look forward to all the belly touching! Xx."
Teigen and Legend, 37, tied the knot in Lake Como, Italy, in September 2013. The "All of Me" singer proposed to Teigen in December 2011 after four years of dating. The two are also "parents" to three furry friends -- Puddy, Pippa and Penny.
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LOS ANGELES, CA - AUGUST 30: Model Chrissy Teigen and singer John Legend arrive at the 2015 MTV Video Music Awards at Microsoft Theater on August 30, 2015 in Los Angeles, California. (Photo by Gregg DeGuire/WireImage)
HOLLYWOOD, CA - OCTOBER 13: Model Chrissy Teigen attends La Mer Celebrates 50 Years of an Icon at Siren Studios on October 13, 2015 in Hollywood, California. (Photo by Jennifer Lourie/Getty Images)
PARIS, FRANCE - JULY 07: Chrissy Teigen and John Legend attend the photocall for the Lancome Celebrates 80 Years of Beauty With All Its Ambassadresses on July 7, 2015 in Paris, France. (Photo by David M. Benett/Getty Images for Lancome)
LONDON, ENGLAND - JULY 06: John Legend and Chrissy Teigen attend day seven of the Wimbledon Tennis Championships at Wimbledon on July 6, 2015 in London, England. (Photo by Karwai Tang/WireImage)
LAS VEGAS, NV - MAY 17: John Legend and Chrissy Teigen arrives at the 2015 Billboard Music Awards at MGM Garden Arena on May 17, 2015 in Las Vegas, Nevada. (Photo by Steve Granitz/WireImage)
LAS VEGAS, NV - MAY 16: Model Chrissy Teigen arrives at 1 OAK Nightclub at The Mirage Hotel & Casino for a special Pre-Billboard Music Award celebration on May 16, 2015 in Las Vegas, Nevada. (Photo by David Becker/WireImage)
NEW YORK, NY - MAY 04: John Legend, Chrissy Teigen, Emily Ratajkowski and Gabrielle Union leave the 'China: Through The Looking Glass' Costume Institute Benefit Gala at Metropolitan Museum of Art on May 4, 2015 in New York City. (Photo by James Devaney/GC Images)
BURBANK, CA - APRIL 26: Model Chrissy Teigen (L) and recording artist John Legend attend The 42nd Annual Daytime Emmy Awards at Warner Bros. Studios on April 26, 2015 in Burbank, California. (Photo by John Sciulli/Getty Images for NATAS)
Chrissy Teigen attends The Comedy Central Roast of Justin Bieber. (Photo by Christopher Polk via Getty Images)
HOLLYWOOD, CA - FEBRUARY 22: (L-R) Chrissy Teigen and John Legend arrive at the 87th Annual Academy Awards at Hollywood & Highland Center on February 22, 2015 in Los Angeles, California. (Photo by Dan MacMedan/WireImage)
BEVERLY HILLS, CA - FEBRUARY 22: (EXCLUSIVE ACCESS, SPECIAL RATES APPLY) John Legend and Chrissy Teigen attend the 2015 Vanity Fair Oscar Party hosted by Graydon Carter at the Wallis Annenberg Center for the Performing Arts on February 22, 2015 in Beverly Hills, California. (Photo by Kevin Mazur/VF15/WireImage)
Actress Chrissy Teigen arrives at the 87th Annual Academy Awards at Hollywood & Highland Center on February 22, 2015 in Hollywood, California. (Photo by Michael Buckner via Getty Images)
LOS ANGELES, CA - FEBRUARY 08: Model Chrissy Teigen (L) and recording artist John Legend attend The 57th Annual GRAMMY Awards at the STAPLES Center on February 8, 2015 in Los Angeles, California. (Photo by Jeff Vespa/WireImage)
Swimsuit model Chrissy Teigen and comedian Adam Devine attend the Sports Illustrated 2015 Swimsuit Takes Over Nashville With Kings of Leon event. (Photo by Rick Diamond via Getty Images)
Model Chrissy Teigen and singer/songwriter John Legend attend the unveil of the Reimagine Learning Initiative during Mercedes-Benz Fashion Week. (Photo by Cindy Ord via Getty Images)
John Legend and Chrissy Teigen celebrates His Birthday And The 10th Anniversary Of His Debut Album 'Get Lifted'. (Photo by Dimitrios Kambouris via Getty Images)
Simon Huck, Chrissy Teigen and Jonathan Cheban attend John Legend Celebrates His Birthday And The 10th Anniversary Of His Debut Album 'Get Lifted' at CATCH NYC. (Photo by Dimitrios Kambouris via Getty Images)
Chrissy Teigen hosts Shutterfly's Wine, Dine and D.I.Y. Design Holiday Event at Sopra on November 11, 2014 in New York City. (Photo by D Dipasupil via Getty Images)
Chrissy Teigen and John Legend attend the White Party Dinner Hosted by Andrea and Veronica Bocelli Celebrating Celebrity Fight Night In Italy Benefitting The Andrea Bocelli Foundation and The Muhammad Ali Parkinson Center. (Photo by Andrew Goodman via Getty Images)
Chef Dominique 'Cronut King' Ansel and model Chrissy Teigen attend as DKNY celebrates the launch of the new DKNY MYNY fragrance with Rita Ora, Chrissy Teigen, Hannah Bronfman, among other notables, at General Worth Square at Madison Square Park. (Photo by Jamie McCarthy via Getty Images)
John Legend, winner of the award for best original song Glory in a film for Selma, poses with Chrissy Teigen, right, in the press room at the 72nd annual Golden Globe Awards. (Photo by Jordan Strauss/AP)