How small is the world, really?

I'm sure you've heard of it many times before. Your friend, A, knows another friend of yours, B, who is halfway around the world. What a small world! Or your aunty finds out that your mother's friend used to teach her art during primary school. Even smaller!

But I bet that there are fewer instances of how small the world can really get, when you've heard my tale.

The basic settings are:

The place? Outside Hermes, KLCC
When? Summer 2004

The situation:
My girlfriend and I were walking around KLCC. She bumps into a friend of hers and goes away to talk with her. I amuse myself looking at the shop displays for a few seconds, look around, and see a familiar face.

Me: *surprise* X! Hello! What are you doing here?
X : Eh hello! I'm here with my sister, but she bumped into a friend...

And he gestures to where my ex and his sister were catching up. The two of us could only look at each another, my face flabbergasted. Understanding of the whole situation at that moment.

That my then girlfriend's friend's brother was my then housemate at a smallish city in the UK. His room was literally right next to mine (We've since moved on, and I have moved to London since then).

Since then, the world appears to be too big, if I can't somehow connect a friend with another. But not that I want it to happen often, anyway.

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If you know of any other similar situations that you were in, do share! :)