The actress, 47, and 40-year-old husband Bejni Madden recently welcomed a baby girl, news the two shared Friday morning on Instagram.
"Happy New Year from the Maddens! We are so happy, blessed and grateful to begin this new decade by announcing the birth of our daughter, Raddix Madden," read a note from the couple (below). "She has instantly captured our hearts and completed our family."
"While we are overjoyed to share this news, we also feel a strong instinct to protect our little one's privacy," the post continued. "So we won't be posting pictures or sharing any more details, other than the fact that she is really really cute!! Some would even say RAD :)"
They closed out their announcement by saying, "From our family to all of yours, we're sending out love and best wishes for a Happy New Year and Happy New Decade!"
This is the first child for the couple, who tied the knot nearly five years ago today on January 5, 2015. They got married shortly after Diaz's longtime friend Nicole Richie -- who's married to Benji's brother Joel -- introduced them to each other.
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In recent years, the actress has stepped back from the spotlight, last appearing in 2014's "Annie."
"The way I look at it is that I've given more than half of my life to the public. I feel it's OK for me to take time for myself now to reorganize and choose how I want to come [back] into the world," she told InStyle earlier this year.
"I don't miss performing. Right now I'm looking at the landscape of wellness and all that," added the now-health book author. "But whatever I do, it has to be something I'm passionate about — something that just feels effortless."
In the same interview, she said that marrying Benji was "the best thing that ever happened to me."
"My husband's the best," she added. "He's the greatest human being, and he's my great partner. Marriage is certainly hard, and it's a lot of work. You need somebody who's willing to do the work with you, because there's no 60-40 in marriage. It's 50-50, period. All the time."