AceShowbiz -

Rob Kardashian and the rest of the famous family's members recently celebrated his birthday in Malibu, but there's someone missing from the party. Rob's girlfriend Blac Chyna didn't get an invite to his birthday, but why?

A source close to Rob revealed the reason why he didn't invite his beloved lady and didn't introduce her to his family. It was said that Rob didn't want any drama on his special day, considering that his sister Kylie Jenner didn't like his relationship with the mother of one. "Rob's also cautious not to have any unnecessary drama affect his romance with Blac. In that kind of setting it wasn't really appropriate for her to be there," the source told HollywoodLife.com.

It was also said that the party was a "family affair," despite the fact that Tyga, Corey Gamble and Scott Disick were in attendance. "It was really a family affair for Rob's birthday get-together dinner, so Blac wasn't invited," the source continued. Tyga and Kylie have been dating for some time now, so maybe Tyga is considered family at this point, unlike Blac.

The Saturday, March 19 party marked the first time that Rob met the 26-year-old rapper since he started dating Blac. Though the two seemingly managed to handle their awkward run-in, Tyga didn't join Kylie, Rob, Kris Jenner, Kim Kardashian and others to take some pictures together.