Gossip Girl star LEIGHTON MEESTER has fired her ex-con mother as her manager and cut her off financially, The ENQUIRER has learned exclusively.

The 24-year-old actress dumped Connie Meester, 54, after her mom was involved in a nasty confrontation that caused a judge to issue a restraining order against her. Connie has an extensive criminal past and gave birth to Leighton while she was serving time in prison for marijuana smuggling.

The new incident – in which Connie allegedly threatened to "hunt down and kill" a former friend – has Leighton worried that her mom is falling back into her old lifestyle.

In recent years, Connie has devoted herself to helping Leighton make it big in Hollywood. But in court papers obtained exclusively by The ENQUIRER, her former friend Laurel Wiig says she threatened to kill her in a chilling phone call. Wiig also claims that Connie "is an addict," although she doesn’t specify what substances she is taking.

On Jan. 31, Connie was hit with a restraining order that bans her from being near Wiig.

"Leighton has always disapproved of her mother’s criminal past, and now that she’s gotten into more trouble, she made the painful decision to cut ties with Connie," said a source close to the star.

Leighton’s latest movie The Roommate opened on top of the box office, and she got raves for starring with Gwyneth Paltrow in Country Strong.

Added the source: "Hopefully, Connie will get whatever help she needs and she and Leighton can sort out their relationship."