"Just fainted in Harrods. #croquemonsieur needed," posted the brunette star, who is reportedly due next month. The new arrival will be her second child with husband Sam Cooper – their daughter Ethel turned one on November 15.
The shopping trip wasn't a complete bust though. "On the bright side, managed to pick up Professor Snape Wand in Ollivanders box and Slitherin pen for Nephew's Xmas present," she wrote, with the hash tag "luckyboy". The little boy is clearly a fan of the Harry Potter film series.
Lily recently mused about the difficulty of dressing to suit her curvier figure. "Hmmm.... What to wear today, or ahem, how to hide my shameful baby bump," posted the pop star on Twitter on the day she was snapped heading to a recording studio to work on her forthcoming album.
The singer officially 'retired' from the music world in 2010, a year after she released her last album, It's Not Me, It's You. She wanted to concentrate the vintage fashion business, Lucy in Disguise which she set up with her sister Sarah Owen as well as enjoying family life. But after she penned songs for the Bridget Jones musical, Lily had a change of heart.
But while she forged ahead on the career front, there were developments in her family life. Reports began to circulate in the summer that Lily was pregnant again, and that the Who'd Have Known singer had been for her three-month scan. This was when her daughter Ethel was just eight months old.
There was no official announcement from the star or her other half, painter and decorator boss Sam, but Lily's dad spoke on their behalf. He simply said: "Yes, she is pregnant," during an interview on This Morning.
The couple are overjoyed about the new arrival. They previously suffered heartbreak in 2010 when Lily lost a baby six months into a pregnancy. She also had a miscarriage in 2008 when she was dating Chemical Brothers DJ Ed Simons.
Lily wed Sam in August 2011 during a traditional country wedding held in Gloucestershire. There was a surprise under her lacy dress by French designer Delphine Manivet – the bride was four months pregnant with baby Ethel.
The singer has described Sam as a "normal bloke" and "the love of my life". She added: "Sam treats me differently. He’s told me he’ll look after me forever. That's what I've always wanted."