Sebastian Telfair's sister just fessed up in court and admitted to threatening to kill the ex-NBA star's estranged wife -- and now, she's facing up to 5 years in prison over it all.
Octavia Telfair had been arrested in May 2019 after federal investigators said she spewed vile threats toward Samantha Telfair.
Prosecutors claimed after Samantha had testified against Sebastian in his gun case ... Octavia felt it was all treacherous, called Samantha repeatedly and left terrifying threats.
Samantha told investigators that Octavia had told her she would "kill my kids and cut my face." Investigators also said Octavia threatened to kill Samantha, her aunt and her siblings as well.
Octavia was initially charged with transmission of threats to injure ... and at a hearing Friday morning, TMZ Sports has confirmed she pleaded guilty to the charge.
"Yes, it was an argument with my sister-in-law, verbal argument," Octavia said on a video conference call with the court. "Yes, I admit it."
Octavia now faces up to 5 years in prison ... though the guilty plea will likely mean she'll spend far less time than that behind bars -- perhaps even no time at all depending on how the judge sees things.
Octavia is due back in court in July for a sentencing hearing.
Sebastian Telfair -- who famously appeared on Sports Illustrated's cover as a high schooler -- played for several teams in the NBA from 2004 to 2015.
He was a Trail Blazer's 1st-round pick in the '04 NBA Draft.