The couple became parents again earlier this year (12) after adopting a newborn baby girl from the U.S. named Adalaide, a sister for their daughter Naleigh, four, who was born in South Korea and was taken in by the stars when she was just nine months old.
But the Knocked Up beauty admits she was caught by surprise at how swift the American approval process was, and they only had days to design her nursery.
She tells U.S. Tv host Jay Leno, "(It) was fascinating because we started the adoption process again and we thought we were gonna adopt internationally. It's a pretty long process. It can take years. And then we started exploring because we had heard that Korea had gotten very hard to adopt from, and China had a very, very long waiting list... And so we started exploring the idea of domestic adoption - just exploring - and then my lawyer called and said, 'There's a birth mother and she's due in four weeks and she's all yours if you want her.'"
Heigl was delighted at the news, but confesses her singer partner was a little more apprehensive.
She explains, "He thought it was gonna be a few years, and that we were gonna end up with more of like a nine-month-old or 10-month-old, and he looked at me and said, 'You're telling me in a month we're gonna have a newborn?'
"And I said, 'Yes. It's perfect timing, don't you think? Look, we're both here, we're not working. This is great. We can spend time with her.' And it has been beautifully serendipitous and graceful, because we've gotten to spend all this wonderful time with her."