The model and actress, 27, announced the happy news via a very sweet message on her website Impossible.com.
St Trinians star Lily posted a picture of a purple dinosaur toy and an old-fashioned spinning top placed beside a yellow post-it note with the words "I am having a baby!' written on it.
Alongside the photo, she wrote: "I am very happy to tell you… The first known impossible baby is being born! I met Kwame when I was in the process of developing Impossible and he offered the most profound gift, to help build the platform.
"After working together for a long time Kwame and I fell in love, and I am very happy to share our news that we are expecting our first child together…"
Fans congratulated the mum-to-be with messages including: "Oh Lily, you will be the most amazing mother :)! Have no doubts about it! Very happy for you. Congratulations :-)!!"
Another said: "It's going to be the cutest baby on the planet."
Lily attended the Elle Style Awards this week, and wore a rather billowing pink dress to the event...
It all makes sense now!
Devon-born Lily famously appeared on the cover of Vogue magazine when she was just 16 years old.
She later made headlines when she chose to interrupt her modelling and acting career to attend university, where she was awarded a Double First in History of Art at Cambridge University.
Not just a pretty face at all!
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