Amy Winehouse is taking legal action against Blake Fielder-Civil's mother, Georgette Civil, for copyright infringement.
According to Now, Civil has been accused of allegedly selling one of the love letters the singer, 25, wrote to Blake while he was in jail.
Spokesman Chris Goodman revealed: "I can confirm that the action is being taken."
Winehouse and Blake, 27, were granted a decree nisi on 16 July ahead of their divorce being finalised.
