The 38-year-old actress and model wrote:
"This was originally going to be a post to tell you how excited I am about flying to Cape Town, South Africa to begin working on Resident Evil: The Final Chapter.
But... My husband Paul and I just discovered that we are expecting another baby!!!"
It is Jovovich's second child with Paul Anderson, the producer of the Resident Evil film franchise. The couple welcomed their daughter Ever in 2007, two years before their wedding in 2009.
Milla also explained how the happy news has caused a few set backs in the filming schedule.
"Between the stunt work and what will become my ever-expanding belly, we didn't think pregnancy and zombie killing are the best combo!," she said. "I imagine the only thing I'll be killing in the near future is an endless supply of cupcakes. Yikes...
"We want to make the best movie possible and that would be extremely difficult, to say the least, in my present condition," she added.
The mum-to-be didn't forget about the film's fans, though and finished by saying, "Before I go, I want to also send one more HUGE thank you out to all my amazing fans who have been so patient waiting for the next installment of the RE franchise! YOU ROCK!"
Milla isn't the only celebrity to announce her pregnancy this week. Former Pussycat Dolls star Kimberly Wyatt also confirmed she is expecting her first child in an interview with Hello magazine on Monday.
More celebrity baby bumps below: