Tristan Thompson's mom Andrea Thompson unexpectedly dies

Tristan Thompson is mourning the unexpected death of his mother Andrea Thompson

According to TMZ, citing sources with direct knowledge, Andrea suffered a heart attack at her Toronto home Jan. 5. Tristan has since left Los Angeles to be with his family.

Khloe Kardashian—who shares daughter True Thompson, 4, and a 5-month-old son with Tristan—joined the athlete to "comfort and help him navigate what will be a very difficult time," a source told multiple publications.

"This was unexpected," the source added. "She was incredibly close to his mother, and like Khloe and the Kardashian family always do, they will come together and support their loved ones in their most difficult time of need. Tristan is the father of Khloe's kids and she and her entire family will always be there for him."

Andrea had a huge impact on Tristan's life, especially as his basketball career grew.

After Tristan was chosen fourth overall in the 2011 NBA draft, Andrea reflected on how her son made it all the way to the pros with help from mom and dad Trevor Thompson.