Edward VIii, then Prince Edward, was invested as Prince of Wales at Caernarfon on what he described as 'a sweltering hot summer day....before some ten thousand people' in July 1911.
Edward, then a midshipman of 16, objected to having to wear a costume for the ceremony of white satin breeches and purple velvet mantle and surcoat edged with ermine, but was persuaded into it by his mother.
Lloyd George, the Welsh Chancellor of the Exchequer, whose idea it had been to hold the ceremony, taught the Prince some Welsh phrases that he could remember years later, among them 'Mor o gan yw Cymru I gyd' ('All Wales is a sea of song') which Lloyd George, whom Prince Edward liked, got him to repeat over and over.
At the ceremony Winston Churchill, then Home Secretary, proclaimed the Prince's titles. (He told him later that he'd practised them on the golf course) then, with the vast ruined castle as a backdrop, King George invested his son, putting on his head a coronet cap as a token of principality 'and into my hand the gold verge of government and on my middle finger the gold ring of responsibility.'
'Then, leading me by the hand through an archway to one of the towers of the battlements, he presented me to the people of Wales. Half fainting with heat and nervousness, I delivered the Welsh sentences that Mr Lloyd George, standing by in the ancient garb of Constable, had taught me.'
The above is from 'A King's Story', the memoirs of the Duke of Windsor, Pages 78-79.
Edward claimed that the ceremony made him realise that he recoiled from being required homage. I think he realised from his teens that he was not cut-out for kingship, and this ceremony spurred this realisation.