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In a caption, which accompanied the snap of her daughter's tiny feet, Naomi wrote: "A beautiful little blessing has chosen me to be her mother.
"So honoured to have this gentle soul in my life there are no words to describe the lifelong bond that I now share with you my angel. There is no greater love."
As she shared the baby news, she tagged her mother, Valerie Morris-Campbell, in the post.
Her mother also penned a tribute of her own online, writing: "Congratulations to my daughter Naomi on the birth of her daughter, I'm beyond thrilled as I've waited a longtime to be grandmother. :heart::heart_eyes: @naomi".
Fans of Naomi - who is due to turn 51 later this week - weren't aware she was due to welcome a baby before the announcement, and she gave no further information on the little one's arrival in her post.
She is also yet to share a picture of the little one, reveal her name, or disclose where she was born.
It comes after Naomi stated back in 2017 that she wanted to start a family, but felt no rush because of the wonders of science.
In an interview with ES Magazine, she said: "I think about having children all the time. But now with the way science is I think I can do it when I want.
"I do want a father figure," she added. "I think it's important. It's the way I feel today, sitting here talking to you".
Meanwhile, in 2018, she told Vogue magazine: "I'd love to have kids. I don't discount anything in life. I love kids and always will.
"When I'm around children, I become a child myself. That's the little girl I don't ever want to lose."
It's not surprising she has kept her little one secret, seeing as Naomi has always remained tight lipped about her personal life.
She has previously been rumoured to have had high profile relationships with Skepta and Liam Payne - though neither relationship was confirmed by the model.
Speaking to WSJ, she previously said on dating: "For me, privacy is important to know each other, and I always worry that my job will not allow that.
"But I have ways. I was taught that by Robert De Niro."
It is not currently known if Naomi is in a relationship or who the father of her child is.
Congratulations to Naomi on her new arrival!
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