Caleb Bratayley's Cause of Death Confirmed by Doctors

— -- Doctors confirmed today that Caleb Logan Bratayley died of an undetected heart condition called Hypertrophic cardiomyopathy, according to Caleb's mother Katie.

The YouTube celebrity, who exhibited no symptoms, died suddenly last month at the age of 13.

Shortly after his death, his parents told ABC News that he died of a heart condition and that the family has a history of Hypertrophic cardiomyopathy.

"The sadness of losing someone you love is unimaginable," Katie wrote on Instagram. "Thank you to everyone who has reached out, your kindness and support continues to help our family. We miss our baked potato everyday. #calebratelife #celebratelife"

The Bratayleys (a pseudonym) have a popular YouTube channel with nearly 2 million subscribers. After Caleb's death, they livestreamed an hour-long memorial service for him on Facebook and momentarily paused their daily vlog updates.

“We know you tune in to watch each day and eagerly anticipate new videos, but ask that you bear with us while we deal with this tragedy as a family,” his mother wrote on Instagram at the time.

Recently, Caleb's younger sisters were also tested for the the condition, which, according to the American Heart Association, occurs when the walls of the ventricles thicken. It is a common cause of sudden cardiac arrest in young people.

"The girls' hearts were just recently checked and thankfully look the way they should right now," Katie added.

The Bratayleys are associated with Maker Studios, which is owned by Disney. Disney is also the parent company of ABC News.