Nick & Aaron Carter's Sister Dies

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Leslie Carter -- the sister of Backstreet Boys singer Nick Carter and his brother Aaron -- has died at the age of 25.

A source tells ET the cause of death is unknown at this time pending toxicology results expected to take at least four weeks. Leslie was brought by ambulance Tuesday to a hospital in the town of Westfield, in western New York, where she was pronounced dead. The source added that the cause of death was likely related to a medical condition and not an injury.

Nick Carter Speaks Out About Sister's Death

A statement released by the Carter family on Wednesday said: "Our family is grieving right now and it's a private matter. We are deeply saddened for the loss of our beloved sister, daughter, and granddaughter, Leslie Carter. We request the utmost privacy during this difficult time."

No details were immediately provided about the cause of death.

Aaron Carter Enters Rehab

All three Carter siblings have been active in the music industry and Leslie had a single on the Shrek soundtrack in 2001. Aaron Carter is currently appearing in the off-Broadway show The Fantasticks.