A cursory internet search doesn't give a definitive answer.
His maternal uncle, the 2nd Marquess of Milford Haven, and maternal grandmother, the Dowager Marchioness, were his guardians at this time I think, and several members of his maternal family are confirmed attendees (both the 2nd Marquess, and Lord Louis Mountbatten [later Earl Mountbatten of Burma]). Several members of his paternal family also attended representing Greece and Denmark, though I don't think he had much to do with that side of his family.
He had attended the Duke of Kent & Princess Marina's wedding in 1934 where he first met the future Queen, so clearly had been at Royal events before. His invitation to that wedding was probably primarily as a first cousin of the bride, rather than a more distant connection to the British Royals themselves.