I would like to know if my son is USA citizen as my (naturalized citizen) ex-husband and I are divorced?

Q: My son and I are legal residents. His dad and I are divorced but his dad is a naturalized citizen as of 8-23-13 and said our son would automatically acquire citizenship. At the time my son was 17 yrs, he is now 18. I have also recently applied for citizenship, but before my son applies, I would like to know if he is a...