Lily Allen is the first celebrity to land an endorsement deal with Cornetto.
The 28-year-old singer mentioned the ice cream brand on Twitter last July, surprised at how few calories the tasty treat contains.
She wrote: "Is it true there's only 190 calories in a Cornetto? #cornettodiet.(sic)"
Although the message was simply "a bit of fun" she is now expected to earn a six-figure sum while she works with Cornetto on their forthcoming advert.
A source told The Sun newspaper: "Lily only Tweeted about the ice cream for a bit of fun - she never anticipated it would turn into a huge endorsement deal.
"The new advert is a love story and Lily plays a doctor. It's all good fun."
Lily - who has daughters Ethel, two, and 11-month-old Marnie with her husband Sam Cooper - previously admitted she used to starve herself before photo shoots but has conquered any insecurities she may have had about her figure and now embraces her body for what it is.
She said: "I felt quite brave shooting the 'Hard out Here' video. In all my past videos and photo shoots I've starved myself for days to get into what I felt was a good enough shape. But in this one, I was wearing leggings!
"And a skin-tight T-shirt and a bra over the top - you can see the bulge! It wasn't necessarily pretty, but I felt very strongly that I wanted to do that. Because I'm a woman now, and I have two babies, and I don't want to hide it."