Happy birthday, Kourt!

The eldest Kardashian sister celebrated her 40th birthday Thursday night at a blowout bash at what appears to be sis Khloe's home. Mom Kris, Kylie and Kendall, Khloe and Kim were all in attendance and even Kourtney's ex Younes Bendjima was invited!

The family planned an over-the-top bash, of course, with some cheeky details including an NSFW cake recreating Kourtney's infamous nude bathtub selfie. And customized Don Julio bottles were engraved for each guest -- Kourt's reading "Most Interesting To Look At" -- a reference to Kim's famous line about her older sis on KUWTK in which she referred to her sister as boring looking!

There was even a surprise musical performance by Robin Thicke!

But back to the most important detail -- the fact that Younes was there. Does that signal a possible makeup?