Publicist Murray Chalmers said Monday that "it is with great sadness that we have to confirm that Lily Allen and Sam Cooper have lost their baby."
He says Allen and Cooper are asking for privacy at a "deeply distressing time."
Allen announced in early August that she was three months pregnant.
The 25-year-old singer, whose hits include "Smile" and "The Fear," had an earlier miscarriage in 2008.
She has been dating 32-year-old painter and decorator Cooper for more than a year.