After the release of the 24-year-old supermodel's three seriously sexy SI covers, Day posted a video to Instagram of herself in a black bikini, encouraging all women to share their swimsuit snaps. "I've been producing the annual Swimsuit issue for 19 years, but today I'm the one in a bathing suit, and here's why," she explained. "This year's issue will showcase the widest diversity of women in SI history. Women of all ages, and shapes, and from many different backgrounds."
Upton was thrilled to see Day's video and reposted it to her own Instagram account. "Thank you @mj_day for always leading from the front and helping to spread the message of confidence, strength, beauty and body diversity!" she wrote. "Honored to have you as a dear friend #preach."
Day -- who teamed up with @WomenIRL to persuade others to share their swimsuit snaps -- admitted that she was initially nervous to post the video. "Deep.Breath. If I'm going to talk the talk, I am going to walk the walk. Please consider participating. It was equally terrifying and liberating for me," she captioned the bikini-clad post, adding the hashtags #WhatIModel and #LoveYourSwimsuit. "Funny how I have spent my life on a beach since childhood and I have never truly felt comfortable in a swimsuit -- even at my thinnest."
Day added, "We need to love ourselves in the present. No matter what. I invite you all to do so."
Supermodel and Leonardo DiCaprio's girlfriend, Nina Agdal, also participated in the campaign, and shared a video of herself in a bikini. "I model swimsuits because it's my job, but I also model health and happiness, which I believe go hand-in-hand. It all starts within," she said. "Everyone is different and everyone is beautiful in different ways."
In addition to Upton and Agdal, Chrissy Teigen, Ashley Graham are featured in SI's 2017 swimsuit issue, as well as newcomer, Hunter McGrady. "I want to thank @MJ_Day for an opportunity like this and for being a force in this industry," McGrady said, praising the magazine's director. "Beauty is not a number. It has no limits. I have never felt sexier than I did in this shoot."
She added, "Women, for anyone who has ever felt uncomfortable or insecure because of rolls, or stretch marks, or cellulite, or acne, or felt like you didn't measure up because you weren't represented in the magazines --THIS IS FOR YOU!"
Here's a look at Tiegen's sexy photo shoot with the SI, below: