The prince and his bride previously confirmed the baby would be born in July, but named no specific due date.
A London newspaper said Sunday the child is on target to arrive July 13, during a four-day festival celebrating the 60th anniversary of Queen Elizabeth II's coronation.
The Clarence House Press Office told ABC News it could not comment on the due-date report, but reiterated, "The baby is expected to be born in July."
NBC reportedly holds celebs hostage to Jimmy Fallon's show
Boston schools pull out free condoms over wrapping complaints