That's a new one on me!

That's news to me.

I never heard of such a thing!

Ex) 

A: Did you hear? They have blocked off Winsor Street for  some repairs.

B: That's a new one on me!

A: 그 얘기 들었어? 보수공사 때문에 윈저스트리트가 봉쇄되었어.

 B: 금시초문인데!