The photo was taken in 1923 at Belgrade deck.
The occasion was marriage of Prince Paul of Yugoslavia to Princess Olga of Greece and Denmark. King George VI (at that time the Duke of York) was the best man at their marriage and godfather to the Crown Prince Peter of Yugoslavia, who was baptized at the same time in Belgrade.
The Duke of York was second cousin of Princess Olga, while his wife the Duchess of York(later Elizabeth, the Queen Mother) was a friend of Prince Paul from his Oxford days, while he was studying in Britain.
Princess Helena Petrovna was related to both families. She was first cousin of Prince Paul, while her late husband Prince Ioann of Russia was first cousin once removed of Princess Olga of Greece and Denmark. Her grandmother, Queen Olga of Greece, who was alive at the time, was her husbands aunt. She was also aunt of Crown Prince Peter(later King Peter II of Yugoslavia).