The Smile singer announced she was expecting her first child with then-boyfriend Sam Cooper in 2010, but she contracted a viral infection six months into the pregnancy and she subsequently lost the baby.
To mark the fifth anniversary of her hospitalisation, she spoke openly about the traumatic experience to her 4.3million Twitter followers.
‘I delivered a beautiful baby boy, but sadly he didn’t make it.’
The song, Something’s Not Right, features on the soundtrack to the film Pan, a live-action version of Peter Pan.
Lily linked her tweets to the donation page for Sands, the Stillbirth and neonatal death charity, and asked people to donate in memory of her late son.
Allen is now mother to two daughters; Ethel, who was born in 2012, and Marnie, born in January 2013.