When Matthew McConaughey and his four-months-pregnant girlfriend, Brazilian model Camila Alves, went in for a prenatal checkup, their doctor slipped up and revealed the baby's sex , Star reports.

"During the ultrasound, the doctor referred to the baby as a 'he,'" a friend tells Star. "Matthew was so upset with the doctor for giving it away. When the doctor realized what he had done, he felt bad and tried to say that he calls all babies 'he.' But he then confessed that wasn't really case after Matthew demanded to know the truth."