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Law & Order: SVU star Mariska Hargitay and husband actor Peter Hermann made headlines last year, when they adopted both their daughter Amaya Josephine and son Andrew Nicolas within the span of six months.

But now Hargitay is opening up for the first time about the unseen heartbreaking moments of the adoption process.

"I'm not gonna lie," Hargitay admits to Good Housekeeping. "There were wrenching moments. I say to everybody, 'Adoption is not for the faint of heart.'"

Mariska Hargitay Adopts Baby Girl

A particularly brutal moment occurred when the couple was able to connect with a birth mother not far from New York City, and after meeting the woman, finalizing the adoption plan, being present in the delivery room, naming the newborn and parenting her for two days, the birth mother changed her mind.

"It was nothing short of devastating," Hargitay reveals. "But … it was probably the greatest, happiest ending. I mean, it was so painful for us, but it was deeply joyful and deeply right for her."

She also calls the decision to adopt their son Andrew so quickly after adopting Amaya a "no-brainer." Though they originally wanted to wait 18 months before adopting a second child, they got the news that a premature baby was ready for adoption and had to quickly make a choice.

Mariska Hargitay Adopts Baby Son

"It was like … a miracle," she explains. "And I don't use that word lightly. I've never made a bigger decision so quickly."

But through all the highs and lows, Hargitay has no doubt that the strenuous adoption process of both Amaya and Andrew (who joins the couple's biological son August) was well worth it.

"Adoption was a bumpy ride -- very bumpy," she admits. "But, God, was it worth the fight."