Unwanted pregnancy

I have been wanting a new baby for a while but my husband doesn't he wants to wait until our son is older so I've been on birth control for a while well I just found out at my check up that I'm about 12 weeks pregnant. I normally didn't get a period with my birth control so I didn't think anything of it when I didn't get one. How in the world do I tell him I'm pregnant knowing how upset he's going to be..