Referring to past spares Princess Margaret and Prince Andrew, Duncan said the one thing they share with Harry is that their roles have never properly been defined.
“They have almost felt their way in the dark and that’s led to problems… we know what those problems are because there’s no official role for a spare,” Duncan said.
“They have to just sit back and watch the elder brother, elder sister become the monarch and that has caused problems, whether it be psychological, or whether it has been problems with alcohol, or problems with very dubious friends, as in the case of Jeffrey Epstein and Prince Andrew.
“With Harry of course, [he got into trouble] wearing Nazi outfits and going to strip bars, but it’s not really their fault - they're stuck in an undefinable role,” he said.
Duncan also told host Kate Thornton: “It's such an unnatural role to be a spare to an heir because, whether we like it or not, it's quite unnatural to still have a royal family.
“It's ludicrous in reality, in 2020, to suggest that Prince George was plucked by God to be king when another child born in the bed next to him in the Lido wing was always going to be whoever it was.”
The royal expert then drew comparisons to the French, who revolted against their royal family in the 1700s – although he clarified he wasn’t suggesting the UK follow suit.
Dr Tessa Dunlop then weighed in on the matter, saying, unlike previous generations, Harry has been forced to navigate being the royal spare without aristocratic support.
“For Harry and William, they can’t see in their friend group the same sort of problems that would have existed over the last 400 years historically where all the eldest primogeniture reigned supreme.
“They don’t have an equivalent support network that was provided by the British aristocratic system – it doesn't help Harry make sense of his effectively pointless position,” she said.