The writer and academic, Sir Arthur Quiller-Couch, wrote much under the pseudonym 'Q' though I'm not sure whether it was initially adopted as a 'disguise'. In his later life the identity of 'Q' was certainly not a secret.
For example, in the lead-up to Christmas 1937, The Times newspaper (22 Dec 1937) promoted a story by 'Q' which they would be publishing on Christmas Eve. The blurb following the headline noted that it had been written by Sir Arthur.
And of course the nom-de-plume was reported in various obituaries (e.g. The Times's on 13 May 1944).