According to the podcast, there was way more to the ensemble than just a gorgeous royal blue suit. Depending on the princess’s shoe choices (specifically, her flats), you could see where her relationship with Prince Charles was at the time.
So, what exactly does this mean? Well, the flats (and the fact that at points in time she made herself look shorter by standing on a lower step) indicate that the couple was in a good place at the moment, as Diana was making sure not to tower over her husband. Because of their similar height, it has been reported that she was even banned from wearing heels in the presence of the future king.
However, when Diana started to break the royal rules, it marked less unity in the couple’s relationship. Take, for example, that infamous revenge dress. At that point in time, Charles had just revealed to the world that he had been unfaithful. Di’s entire ensemble, including the black stilettos, made quite the statement because that kind of attire wasn’t usually appropriate for certain events—and she no longer seemed worried about being taller than her husband.