Karen Houghton - the younger sister of Kris Jenner - died on March 18 at the age of 65 from "cardiac arrest and sudden cardiac arrhythmia".
TMZ reports that her death certificate also listed Type 2 diabetes as a secondary underlying cause.
Kris announced her sister's death with an emotional post on Instagram in March.
She wrote: "It is with the heaviest heart and deepest sadness that I share that my sister Karen passed away yesterday unexpectedly.
"My heart aches for my mom MJ (Mary Jo) and my niece Natalie and I pray that God guides us all through this difficult time. Karen was beautiful inside and out."
Kris also hailed her late sister as the "sweetest, kindest, the most sensitive and vulnerable" person who she said was also "so so funny".
She added: "She always felt grateful and thankful for her life and treasured her family and friends and especially her beautiful daughter."
Adding that Karen holds a "huge part of (my) heart", she said: "I cherish every single memory we have together."
Kris concluded her message with the lines: "Karen's passing is a reminder that life is so short and precious and tomorrow is never promised.
"We must tell those we cherish how much we love them. I love you my beautiful sister."
And, Natalie explained that her mother's death happened "so quickly".
She posted: "Dear Mommy, I can't believe your gone. This doesn't even feel real. I keep hoping that I will get to hug you or kiss you or hear your voice one last time.
"You were my best friend, my everything. The best mother a daughter could ever ask for and I'm so grateful to have had a mother like you.
"You were the most kind, sweet, loving, giving, and caring soul. You had the biggest heart.
"And I don't know how to go on without you. It all happened so quick [and] I wasn't ready for you to go.
"An angel was sent to heaven on March 18th, 2024. I love you mommy and you will forever be missed."