Khloé Kardashian was ''too upset'' to attend North West's birthday.

The 'Keeping Up With The Kardashians' star was noticeably absent from her niece's second birthday party in Disneyland and reportedly skipped the bash after learning about the devastating loss of her estranged husband Lamar Odom's best friend.

A source told E! News: ''Khloé was too upset over Jamie dying. She wasn't there.''

Instead, Kris, Kylie and Kendall Jenner, Kourtney Kardashian and her son Mason, five, and Kylie's boyfriend Tyga were on hand to celebrate with North and her parents Kim Kardashian West and Kanye West.

Khloé was one of the first people to reveal the tragic news that Jamie Sangouthai - who was one of the best men at her and Lamar's 2009 wedding - had passed away from an alleged heroin overdose.

She wrote on Twitter alongside a broken heart emoji: ''When does it stop? RIP Jamie Sangouthai.''

Lamar is believed to be ''beside himself'' by the loss.

A source said: ''Lamar is beside himself. This is the worst tragedy.

''This is so sad. They were best friends, like brothers. Lamar is going to take this really hard.''