According to Variety, Zellweger, 40, is expected to start filming at the end of this year. The third installment of the comedy will center on the British publishing exec's attempts to have a baby before it's too late.
Zellweger, who won a Best Supporting Actress Oscar for Cold Mountain, was nominated for 2001's Bridget Jones's Diary and also starred in the 2004 sequel, Bridget Jones: The Edge of Reason. For the roles, Zellweger famously had to pack on about 30 lbs.
"Can I just tell you my body is whacked by the time we finish one of those?" she told the British Daily Mail of gaining weight for the films. "It doesn't know what has happened because it thinks there's supposed to be a baby and there's no christening."
Overeating was fun at first, she said. "For two days it's bliss ..." she told the paper. "Then after a week your glucose levels are going crazy. You're up and down and all over the place. It doesn't feel good, and no one wants to hear that, but it's the truth."
Trying to shed the weight wasn't fun, either. Said the actress, "It was horrible. On one side it's fantastic because you get to go back to taking care of yourself, so you feel wonderful, but the first lap around the track I felt like I had a toddler on my back."