Sometimes, royals really are just like us. Case in point: following her engagement announcement photoshoot with King Charles , Princess Diana reportedly ate fast food from McDonald's with two royal staff members. In his book A Royal Duty , Diana's former butler, Paul Burrell , recalled retrieving a Big Mac for the princess after watching her photoshoot with King Charles take place. According to Burrell, buying a Big Mac for Princess Diana was the idea of fellow staff member Mark Simpson, who told him, "We could have a little picnic and brighten up her day. Come on, let's go to McDonald's." "I was too frightened to join Mark on his mission and anxious about how Lady Diana would respond," Burrell wrote. However, "having delivered his Big Macs, [Simpson] came back to fetch me, after checking the coast was clear." Despite being concerned a senior royal might find out, Burrell decided to join Simpson and Diana.…