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Portland State linebacker AJ Schlatter died at the age of 20 on Sunday at approximately 9:15 p.m. PT because of an apparent blood clot.

Schlatter's father posted on Facebook about his son's death Monday, explaining the blood clot may have occurred following surgery to remove his tonsils, which he underwent Friday:

Per the Vikings' official website, Schlatter appeared in 11 games and started 10 this past season, racking up 62 tackles (6.5 for loss), two fumble recoveries, two sacks and an interception.

The Oregonian's Ken Goe passed along statements from Vikings head coach Bruce Barnum and athletic director Mark Rountree.

"My heart is with the Schlatter family. They are our focus right now," said Barnum. "We lost a diamond that will never be replaced. He was the definition of what we are about at PSU."

Rountree offered condolences to the Schlatter family in his remarks:

Our thoughts and prayers go out to the Schlatter family with all the compassion and sympathy we can bring to bear during this difficult time. Things like this aren't supposed to happen. We cherish every student's well-being, and the loss of AJ will be tough on our family. He represented his family and Portland State with passion, courage, and humility that made us all proud. He will be missed.

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Per Goe, Schlatter's father was an assistant football coach for the Vikings in the 1980s. His mother, Terri Jo, played volleyball at Portland State, as did his sister, Garyn.

After redshirting during the 2014 campaign, Schlatter burst onto the scene for an exceptional Portland State team that clinched a berth in the FCS playoffs with a 9-3 record.