I Think I Am Being Bribed (my First "big" Bribe!).

I work in Georgia (U.S.) for a company that owns a large amount of land. I am responsible for maintaining real estate, timber, conservation, property tax, etc. cash flows for all of the company's property. I am the only employee with this scope of work, and all land related transactions go through me. In the recent past I sold a tract of land to, say, "Larry". Larry is a local who comes from old money and invests in long term commercial property opportunities. Since that sale, Larry has been calling me periodically trying to convince me to sell him another property in the same vicinity. This property is not one that we have ever advertised for sale and is highly valuable to our other business operations. Well, this week Larry finally let his shady side show and, I believe, crossed a very important line. Larry offered me, personally a $40,000 "cash signing bonus" strictly to _PMMEYOURSOUL_ on top of the sale price to the company. Larry made it clear that this would be a cash ("we don't write checks for this sort of deal") transaction between him and myself. As I said in the title, this really feels like a bribe and honestly theft on my part. I quickly ended the conversation and said we will talk next week. I clearly see red flags all over this and have no intention of accepting this "deal". My questions are. Is this in fact a bribe? If so, is it safe to assume this action is illegal? Finally and most importantly, should I disclose this information to my boss? I am most interested in the last question since I want to do right by the company I work for (I am a company man). But, would it be wise for me to reveal to my boss that these types of offers are (now) a real thing I encounter, potentially causing suspicion of any other foul play? Thanks in advance, stay frosty out there.