July 28, 2012 14:28 IST
The model - who is married to actor Matthew McConaughey - signed on as the face of department store Macy's I.N.C International Concepts' campaign in April, and discovered shortly thereafter that she was pregnant with her third child.
She told People.com: "A week before we were supposed to have a photo shoot, I found out I was pregnant!
"I was over the moon, but my first reaction was that it was going to be a deal-breaker for the campaign -- that they wouldn't want a pregnant mum -- but we worked it out."
Her 42-year-old husband will portray an AIDS patient in his upcoming film The Dallas Buyer's Club, which begins shooting in September, and the pounds he's lost for the part have become noticeable, according to 29-year-old Camila.
She explained: "He's losing weight for his new movie and he still has to lose more. But I'm very supportive. I'm usually the one right there saying, 'You can't eat this, you can't eat that,' but he's very disciplined. He's really great at it."