The art consultant proposed to Barrymore in Sun Valley, Idaho on the night of his parents' 40th wedding anniversary - but the couple had little time to savour the moment after learning the baby news.
Opening up about the magical chain of events during an at-home interview on U.S. TV show Oprah's Next Chapter, which aired in America on Sunday (20Jan13), Kopelman said, ""We came back home and I'd had this ring in my snowboard bag, and I'm like, 'I think now's a good time.' But also I was like, 'I don't want to not be engaged to this woman for another day longer.'
""We came back to our little condo and I proposed. We get home, we tell our friends that we're engaged and we have about three-and-a-half weeks of enjoying the bliss of engagement... and then, all of the sudden, I get a phone call. I'm at work, and she's like, 'You have to come home immediately.'
""I said, 'Is everything OK?' and she's like, 'Yeah, just get here.' My office, at the time, was, like, five minutes from our house and that five-minute drive felt like 50 minutes... I run home... and she just kind of walks me upstairs and she shows me this pregnancy test. I didn't know what to think.
""We both were over the moon. And then all of the sudden we're like, 'OK, so do we get married this year, or do we not?' And we sat down and we said, 'Let's do it.'""
The couple jumped into action to plan its nuptials, and in June, 2012, a heavily pregnant Barrymore tied the knot with Kopelman in the backyard of their Montecito, California home, so their then-unborn daughter Olive could always feel a special connection to their big day.
The Charlie's Angels star added, ""I wanted Olive to look in the backyard one day, if we're lucky enough to keep this house, and be like, 'We got married right there and you were there, in my stomach!' I thought it would be nice to have a place that we could possibly go back to, as opposed to a place we couldn't.""