Rob Kardashian blocked his sisters and Blac Chyna on Instagram.

The 29-year-old reality star got into heated argument with Khloé, Kim, and his fiancée - who is currently pregnant with the couple's first child - after he failed to attend his grandmother's 82nd birthday, and subsequently removed them from the picture sharing website in response.

On the latest episode of 'Keeping Up with the Kardashians', 32-year-old Khloé asks her brother if he's still going to their grandmother's birthday bash.

He said: ''I can't go to the horse races. I don't want to wear this shirt and shorts and sandals. I don't feel comfortable... because of my weight. I might go, I might not.''

Khloé then asked: ''It's your grandmother's 82nd birthday, how could you not come?''

To which Rob replied: ''I don't know.''

Later on in the episode, 36-year-old Kim stepped in to try and get Rob to attend the birthday celebrations, and Rob eventually agreed under the proviso that he gets a stylist and new clothes to wear.

Kim told him: ''We can find a stylist to get you stuff. I think you have to, for your own soul, [you need to] be getting up and getting dressed and get motivated.''

But when the time came, Rob - who had then taken to Instagram to block the majority of his family - was a no-show to the event and even left 28-year-old Chyna to attend the bash on her own.

Kim said of her brother: ''If you don't want to come, say you don't come. Stop making excuses. That's what pisses me off about him.

''It's so nice that Chyna made this effort to come down and spend my grandmother's birthday with us.

''This is how he's been for the last three years. I don't even know what the answer is.''

After the party, Kim and Khloé paid Rob a visit, and the sock entrepreneur admitted he had missed the party because of a ''disagreement'' with Chyna.

He said: ''I just didn't want to hear from anyone regarding anything... I went to Vegas instead. I just didn't feel like going because me and Chyna got into a disagreement. So, she just gave me a reason to not want to go to with her to San Diego.

''Like, with you guys, it just gets very dramatic.''