While we're all familiar with Kim's pals like Jonathan Cheban, Serena Williams, Rachel Roy and Brittny Gastineau to name a few, it's not often we see or hear about Allison.
But yesterday, Kim took to Instagram to wish her BFF a very happy birthday.
Kim wrote: "Happy Birthday to my best friend Allison. We've been through it all together & there's no one else I'd rather experience it all than with u. I can't wait to achieve our goal."
Hmm.. wonder what the goal is?!
Her post was accompanied by a very sweet picture of a tiny Kim holding hands with a tiny Allison. Aww!
Now, if you're wondering why we rarely see Allison when her best friend is arguably the most famous person in the world, there's a very good reason for it: she doesn't like the limelight.
Biographer Sean Smith writes in his book Kim that the girls have been best friends since school, and that Allison's mother Shelli is close friends with Kim's mum Kris. They all lived near each other in Beverly Hills.
He writes: "Kim has always been respectful of Allison's desire to keep a low profile and the pair are seldom pictured together, even though they still speak all the time. Kim often says that she and Allison 'met the day I was born' and leaves it at that. Other friendships with equally famous people may receive far more publicity but Allison is her oldest and dearest."
(As an FYI, if you're a bit Kim-obsessed like us, then definitely check out Sean's book! It gives loads of info about Kim's life before fame and what it's really like living as a superstar.)