Thanks for your reply.
I wondered if I (as the sponsor) needed to submit the divorce decree for my previous marriage because I didn't see any specific direction in the I-864 instructions or I-485 instructions to include it (of course I could have missed something). I also thought the fact we are submitting Form I-797 showing my fiancée was approved for a K1 visa meant that my marriage eligibility was already established and therefore, I didn't have to submit the divorce decree.
Based on your answer, I will include my divorce decree in the package I submit to USCIS. Thanks again for your help.