London, Aug 25 : Singer Amy Winehouse has sued her former mother-in-law for selling a love letter she had written to her ex-husband Blake Fielder-Civil.

The note was apparently written when her former flame was jailed for assault and perverting justice.

Furious, the Grammy Award-winning singer has reportedly filed for copyright infringement, and asked for 50,000 pounds compensation.

"Amy was furious the private letter was used to make money," the Sun quoted a pal as saying.

However, no date has been set for a hearing as yet.

Winehouse had married Blakein 2007, but they divorced in July this year. (ANI)