LONDON — Many Londoners are proud to be part of a city that is both very English and exceptionally multicultural. So when the comedian and Monty Python star John Cleese questioned the city’s Englishness in a Twitter post, London’s defenders rose up on social media.

“Some years ago I opined that London was not really an English city any more,” he wrote on Twitter on Wednesday, adding that “virtually all” his friends from abroad had confirmed his observation.

The 79-year-old Mr. Cleese left Britain for the Caribbean island of Nevis last year, a decision he said was based on a general disappointment with Britain — specifically the “lying and triviality” of British newspapers and the “depressing” standard of debate around Brexit. (Mr. Cleese voted to leave the European Union in the 2016 referendum.) “I note also that London was the UK city that voted most strongly to remain in the E.U.,” he added in his tweet.

Those who found the tweet disturbing included Mayor Sadiq Khan of London, who became the city’s first Muslim mayor in 2016 and has been a fierce defender of London’s multiculturalism.