Amherst 6.10.1805 at Lord Holland's
Probably William Pitt Amherst DNB 1773-1837. The DNB says very little about this part of his life, he had inherited the title Baron Amherst in 1797. I consulted a few books on the Holland House circle (Sanders, MItchell &c) but found no mention of him as a  part of it, nevertheless the identification seems probable