An interesting extract from the book "Rytterkongen", translated by the poster Stig:
https://members3.boardhost.com/scandinavia/msg/1681317670.html
Robert Prentice says much the same in his biography of Princess Olga, written with her family’s cooperation, who gave him access to family letters and diaries.
Here’s a summary of what he writes:
Frederik proposed to Olga almost immediately after meeting her at Cannes in February 1922. The meeting wasn't accidental. Olga's uncle Prince Christopher had invited Olga, her mother and sisters to stay with him in Cannes while Frederik was "conveniently" there to visit his maternal grandmother, Grand Duchess Anastasia of Mecklenburg-Schwerin, who was Princess Nicholas's cousin.
Olga accepted his proposal, which was followed by Frederik's visit to Athens in March, when he presented her with an engagement ring. But the visit wasn’t a success, as Olga’s mother reported in a letter to Frederik’s mother Queen Alexandrine: “Rico, instead of trying to know and understand her better, was often a little rough and off-handish with her telling her little things that hurt her feelings…” The sensitive Olga became “silent and seemingly cold till Rico thought she didn’t care for him anymore and they both ended by being cold and indifferent to each other…” Olga subsequently “had it out” with Frederik who on the day of his departure informed Olga’s parents that he no longer wanted to marry her. They told him not to make a rash decision and encouraged him to continue writing to Olga as “through letters one often comes to know each better than by talking.” Frederik asked that nothing be said to Olga about this discussion.
Both sets of parents agreed the couple should meet again, which they did in a private, 45-minute meeting in Paris on September 11. Prentice writes: “Unsurprisingly, given his previous attitude in Athens, Rico had decided that the romance could not be salvaged and when Olga tried to reach out to him, he was crushing in his repost and ‘said he had no more love for me.’ With the decision made, she returned the engagement ring to Frederick and observed philosophically that his love ‘couldn’t have been very strong while it was there.’” On September 24 the Danish court announced that the engagement had been broken off “by mutual arrangement.”
According to Prentice, Olga later implied that she had broken the engagement, but “this may have been to help her deal with the pain of rejection, for even some fifty-five years later, as she browsed through her 1922 diary, Olga could still clearly recall ‘the distress it caused me.’”
Prentice also writes: “There is an final interesting footnote to this story: Olga’s parents apparently ‘accused’ her cousin Irene of ‘spoiling’ her chances of marriage with Rico during his stay in Athens. This was something Irene always ‘flatly denied.’ However, there may have been some truth to this story, as Irene later revealed to Olga ‘par hasard one day, that Rico had written to her a proposal, after our engagement was broken off, the first time she ever mentioned such a thing to me!’”
Source: Robert Prentice,
Princess Olga of Yugoslavia: Her Life and Times (Grosvenor House, 2021), pp. 43-46