You ask him to stay at the palace for few days while you discuss the matter with your courtiers.
"But of course, I accept your generosity, Emperor." And so for the next two nights, your palace is hosting Prince Tum Brah and his entourage. The Simians take special liking to the foodstuffs and kitchen maids.
Prince Tum Brah is not interested in conversing with you, and prefers company of his trusted aides and guards.
4*
Meanwhile, Spymaster's agents have been working hard.
They've obtained enough evidence to point that Simian Empire has secured its eastern borders, and that a large-scale campaign is being prepared to strike the Damdamians through Ysirene, next year or the one after it. Unfortunately, drunken servants of Prince Tum Brah aren't that forthcoming in divulging further plans or details of Ysirene attack. That, or the agents were asking the wrong ones.
Two days pass...
The Marshal presents his report - indeed, if horses will be forked over to Simians, there will be a certain shortage of horses for new recruits. This won't stop the recruitment altogether, of course, although the slowdown in training of new recruits will be noticeable in the accounting papers.
An hour later, Prince Tum Brah is summoned to the audience hall, and he shows up with part of his entourage.
"So I am here, Emperor Houlandin." Prince Tum Brah clasps his hands, standing before you with a smirk and playful spark in his eyes. "Do tell me, can my father have the horses our Empire needs so much?"
A) Agree to the request and promise five hundred horses each year to be sold to Sim Empire.
B) Politely decline Prince Tum Brah's request, for Methiant itself needs its horses.
C) Politely decline Prince Tum Brah's request, and ask whether some money, instead of horses, would be accepted by Mahjar Sim.