In February of this year the BAFTA-award-winning star excited fans with the news that she was pregnant with her third child.
Whilst the Broadchurch actress has kept us guessing with no formal announcement of the birth, it now seems Olivia may have let the cat out of the bag.
On Tuesday evening, Olivia, 41, appeared on the red carpet without any sign of a bump.
Arriving at the London Film Festival for a premiere of her new film, The Lobster, it was the first time the Norwich-born actress has broken her low profile in months.
The Sun had previously reported that the baby was born in August, but with no formal announcement, was this the confirmation that fans have been waiting for?
Olivia appeared to be bump-free at the premiere of her new film, leading to speculation that she's already welcomed her third child!
Olivia, who already has two sons, Finn, nine and Hal, seven, with her husband Ed Sinclair, said in February that the family were 'very excited' to welcome a new baby.
On the prospect of working whilst pregnant Olivia, who rose to fame in Channel 4's Peep Show, said: 'Obviously, the baby is my priority and we're all very excited.'
'I'm very fortunate that work and family are thriving at the same time. I feel very, very lucky.'
During her pregnancy with her second son, Hal, Olivia said; 'It would be worse if I was having to hide it on screen because I've already got a waddle. But, so far, it's always worked out for me that I've been able to be pregnant in the job I'm doing.'
It was only last month that fellow British actress, Carey Mulligan, made an appearance at the London Film Festival, also bump-free, to promote her new film Suffragette.
Unfortunately everyone forgot that Carey had been pregnant for nine months and no one quizzed her on her newborn at the time, but she's since revealed the gender and name of her baby!
All we can say is congratulations Olivia and we can't wait to see pictures!