Ok hear me out...
In March of 2015, Ronda Rousey showed up at Wrestlemania unexpectedly and caused a lot of buzz for WWE and drew a lot of attention to the event, and even helped generate some UFC appeal among WWE viewers, despite the fact that Rousey was still under contract with UFC.
Now, Brock Lesnar is suddenly appearing at UFC 200 for 1 time only, and will bring huge buzz to UFC, despite the fact that he is still under contract with WWE.
Do you think Zuffa and WWE negotiated a deal to have Ronda show up at Wrestlemania for 1 night in exchange for a Brock Lesnar return at 200?