As the monarch, King Charles is able to request pretty much any food item he desires. But according to a former royal chef, The King previously had several important "instructions," and he didn't like deviating from one breakfast habit in particular.
During an appearance in Channel 5's Secrets of the Royal Kitchen documentary, former Royal Family chef Darren McGrady revealed that Charles especially enjoyed eating fruit from his own garden at Highgrove House. "The instruction was to put two plums and a little juice into the bowl, and send it in to him for breakfast," McGrady said (via Hello! magazine).
