Jamie, who appeared on E!'s "Khloe & Lamar", died in a hospital in downtown LA of possible heroin overdose, TMZ reported.
On hearing the news, Khloe took to Twitter to pay tribute to her friend.
"When does it stop? RIP Jamie Sangouthai," she wrote, adding a heartbreak emoji.
She later tweeted, "Life doesn't get easier but I promise you that life will make you stronger," along with a link to an Instagram picture of a crying woman.
Khloe's friend Malika Haqq also remembered Jamie.
Jamie was Lamar's best friend since high school. He served as one of Lamar's best men during his wedding to Khloe in 2009.