Hilaria Baldwin recently welcomed daughter María Lucía via surrogate after giving birth to son Edu in September

Hilaria Baldwin's youngest is now 1 month old!

The mom of six, 37, shared a sweet photo of daughter María Lucía Victoria, nicknamed MariLu, on Instagram, showing the baby girl smiling to celebrate the milestone. "Happy one month to our happy girl. We love you Marilu," Hilaria captioned the post.

Hilaria and husband Alec Baldwin, 62, also share sons Eduardo "Edu" Pao Lucas, 6 months, Romeo Alejandro David, 2½, Leonardo Ángel Charles, 4, and Rafael Thomas, 5½, and daughter Carmen Gabriela, 7. (Alec is also dad to 25-year-old daughter Ireland.)

After giving birth to Edu in September, Hilaria announced earlier this month that she welcomed a newborn baby via surrogate. The internet quickly went abuzz with questions about why the pair opted for surrogacy and why they did so given Hilaria would have already been pregnant with Edu at the time.

A source previously told PEOPLE, however, "It's no one's business about a woman's right to choose how and when she expands her family."

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A source recently told PEOPLE that the mom and dad are "so happy and spending time bonding together as a family," adding that "Lucía's big brothers and sister are all excited to have a new sibling."

Back in September, when he appeared on Conan after Edu's birth, Alec indicated that he felt he was done expanding his family. The actor also mentioned that the baby that Hilaria lost in a miscarriage in November 2019 at four months pregnant was via IVF when she was trying "for a girl."

On Instagram earlier this month, Hilaria shared a sweet photo of her youngest two, explaining how their arrivals mean even more coming after the previous pregnancy loss.

Hilaria Thomas Baldwin Instagram
Credit: Hilaria Thomas Baldwin Instagram

"Our hearts are filled with so much gratitude. The Baldwinitos craved so much to have a little sister," she began the caption. "Many of you may remember the loss of their sister at 4 months in the end of 2019. There isn't a day that goes by where we don't ache for our daughter. When I found out our baby had died, I told our children that their sister was going to come, just not at that time."

"Nothing will ever replace her, but two wonderful souls have come into our lives, and we are humbled to know them," continued Hilaria. "Our children were brave during our time of tremendous grief — braver than us...and they held out hope. To experience and accept life's ups and downs is challenging, but a reality that all of us have no choice but to receive and process. I have learned that often our children are wiser than we are and their wisdom has guided us."

Hilaria said Edu is their "rainbow baby" and "such a blessing." She added of her newborn daughter: "We are living each day, bonding, and grateful for all of the very special angels who helped bring Lucía into the world."