HELP!!! I found out today that im 4-5 weeks pregnant!!!! how do i tell my fiancee?

Today, i found out my pregnancy. I Did 4 tests and they all said positive, and it makes sense as we has unprotected sex on the 21st May. We already have a 3 year old son named Caleb Elijah. It wasn't really planned, however we had talked about trying for another baby. I am 27 and my fiancee is 29, and we feel its the right age to try again, now that my son is starting nusery. He is away working and doesnt come back until the 21st June. What can i do to suprise him nicely??!!