Sign on bonus from company different from my W2 form

I have a sign on bonus on a 1099 MISC from an employer that I will be starting with in September. My contracts are already signed but I am not CURRENTLY working for them. DO I file it as a bonus from my employer or from someone other than my employer? To clarify I am currently working for another group. My W2 is with them. I don't have a W2 from the company that sent me the 1099-MISC.