Burglars broke into Ashley's Surrey flat this week while he was away with the England squad, and stole love notes, poems and two packets of letters from Cheryl, reports the Daily Star.
The former couple, who finalised their divorce last week, are now said to be worried that the thieves will expose intimate marriage details contained in the letters.
A source said: "Cheryl’s written lots of stuff to Ashley over time while she was touring with Girls Aloud and on the other side of the world with work commitments.
"Their paths didn’t cross as much as they would have liked so they tried their best to be romantic in other ways. Notes, little poems and letters were a big form of Cheryl’s communication and this could all be published soon."
They added: "There are lots of secrets that no-one knows a thing about."
It is believed that the thieves also stole jewellery, cash and the keys to Ashley's sports car.
