Today's phrases is "small world".
You can say this when you are surprised to meet someone you know.
A. Hi Jun! What are you doing here?
B. I work here.
A. Really? Me too! Small world!
A. Hi Jennifer! What a surprise to see here here in Singapore!
B. Yes! It's a small world! I'm here on business. How about you?
A. I'm visiting some relatives.