11:14 AM PT -- Parma PD tells TMZ ... Kagney Linn Karter's mother is the one who called in to report the suicide, and we're told there was a note left at the home where this occurred -- although, cops say they don't know the contents of it.

We're told there's no sign of foul play, and no signs of drugs were found at the scene. It's unclear who the shotgun that was used belonged to.

Kagney Linn Karter's suicide was as horrific as one could imagine -- involving a self-inflicted gunshot wound ... from one of the most high-powered firearms around.

According to Cuyahoga County officials, the former porn star died by suicide last week -- and her official cause of death is listed as an intraoral shotgun wound. What that means in layman's terms ... she put a shotgun in her mouth and pulled the trigger.

No other details about her death have surfaced just yet ... but Parma PD is investigating.

The gruesome update is absolutely gut-wrenching for her loved ones and fans, no doubt -- and it appears to have come out of nowhere ... especially when you consider she'd posted a happy photo from a beach in Florida just a few days prior to the incident.

Of course, since leaving the porn biz behind ... Kagney had moved to Ohio, where she opened a pole dancing studio and had become friends with other people in the community.

Her friends started a GoFundMe for her mother, who's handling funeral arrangements.

In the GFM description, Kagney's inner circle claims she'd battled mental health issues for years -- something her immediate family hasn't commented on or confirmed. If true, though ... it would certainly help explain the tragedy. On the face of things, she seemed OK.

On a grim note, word of Kagney's suicide happens to fall on a noteworthy date. Tuesday marks what would've been Kurt Cobain's 57th birthday ... and he, too, died by suicide under similar circumstances. Kurt took his own life, and also used a shotgun to the head.

A purported autopsy report circulated last month claiming to have the full gory details of Kurt's death scene. We haven't been able to confirm the authenticity of it, but it looks real.

In any case ... it's absolutely terrible to hear, and counts as yet another high-profile suicide.

RIP

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