He could be a noble, just not his primary occupation.
Based on the prior hints QM has given it's either famous for politics/government, but not a politician, or famous for military exploits, but not a high-ranking officer. It could be a civil servant, a jurist, someone who did something famous in one of the wars, etc. - very large number of possibilities. Since Hugh Grosvenor was "warmer," I'd lean towards the government route.