Prince Charles and Camilla are said to have broken royal protocol by signing their names on a nightclub wall last week.
The couple went to London’s 100 Club on Thursday, a basement club where bands like the Sex Pistols, The Jam and Oasis have played.
It comes as some gig venues and theatres are starting to reopen for socially-distanced performances after London went into tier two following Wednesday's lifting of the national lockdown.
When at the 100 Club, Charles and Camilla added their name to a graffiti wall which is part of a musicians celebrity tradition at the venue.
But some are viewing that as a faux pas due to advice told to royals that they should not give out their signature because of the risk of it being forged.
Prince Charles once broke the rule by writing "Charles 2010" for a fan in 2010, but for the most part the family is told to decline all requests for signatures.
During Thursday's visit, to offer their public backing to the struggling nighttime entertainment industry, The Duchess of Cornwall recalled her youth in the Sixties.
After a performance by singer-songwriter Emily Capell and drummer Matt Cowley, Camilla spoke of being a fan of The Faces and Rod Stewart when she was younger and also joked about the "pain" of having a beehive hairdo.
The duchess said she had seen them live and even asked Sir Rod to perform at her husband's 60th birthday party.
She also complimented Capell on her beehive hairdo and joked: "I used to have my hair like that in the '60s so I know your pain."
Turning to Charles, Capell said: "And you like The Three Degrees, sir?"
Charles, 72, who was rumoured to have been romantically linked with Three Degrees singer Sheila Ferguson, laughed and said: "That was a very long time ago."
The Royal couple also went to the Soho Theatre to watch an excerpt from a one-woman show.
In May, Charles raised concerns about how orchestras and theatres would survive the coronavirus crisis.
As he toured the sites on Thursday he said he was "praying" entertainment venues would be able to reopen soon.
The 100 Club has played host to many legendary performers including the groundbreaking scenes of the blues, the birth of punk, the arrival of Northern Soul and the arrival of the indie revolution and performances by Suede and Oasis.
