The Knole guidebook mentions that he worked as a page in the household of John Frederick Sackville, 3rd Duke of Dorset (1745-1799) and that he attended Sevenoaks School.The boy had been brought to England from Guangzhou (Canton) by the Duke’s old schoolfriend John Bradby Blake (1745-1773), who worked for the East India Company.
However, when I did an online search for Blake I found out that he was a keen naturalist and that he had brought the boy, called Huang Ya Dong, to England because of his knowledge of the propagation and use of Chinese plants.
Huang became a minor celebrity, advising Mrs Delaney and the Duchess of Portland on Chinese plants, Josiah Wedgewood on porcelain manufacture and the physician Andrew Duncan on acupuncture…
It is not known what happened to Huang subsequently – he may simply have lived out his days as a servant at Knole (where he was known by the other servants as Warnoton). Perhaps he followed the 3rd Duke to Paris when he was appointed ambassador to the court of Louis XVI.