The portrait is the first painted of the king since his coronation just over a year ago and was unveiled just a few weeks ago.
In a video that is being shared on social media, two activists can be seen attaching two marks to the painting using paint rollers. One of the badges represents the British animated character “Wallace”. The second depicts a speech bubble with a message about the UK animal industry.
According to the owner of the gallery, the painting was not damaged by the action, as it was protected by plexiglass. According to him, the marks were up for no more than ten seconds.
The incident has been reported to the police.
The painting is exhibited in a gallery until June 21.