Does anybody know the exact reason for her failed engagement to the then-Crown Prince Frederik (future King Frederik IX) of Denmark? I've read a couple of biographies, but the explanation is still somewhat murky.

Had fate dictated otherwise, she (and not Princess Ingrid of Sweden) would have become the eventual queen -- and somebody else would be sitting on the Danish throne as the reigning monarch today. It's anybody's guess as to what kind of children the hypothetical couple would have had, and whether there would have been a change to the succession law.

Olga seems never to have lost the twinge in her heart over the missed opportunity to land a crown. Indeed, she wrote wistfully of the 1964 marriage of the newly enthroned King Constantine II of the Hellenes and Princess Anne-Marie of Denmark: "So it seems that another link is being formed between those two royal houses. And to think that it could have been through me ..."

A photograph of a royal gathering in the 1960's shows her head in the direction of, and her eyes facing, the man who might have become her husband. Her family seemed to be hit by bad luck, when it came to near-misses of becoming queens. First, the 1922 engagement between Olga and Rico got broken off.

Then, she failed to catch the eye of the Prince of Wales (the future King Edward VIII of Great Britain), despite her family traveling to England in the hopes of her nabbing him as a husband -- having to settle instead for Prince Paul of Serbia. The British heir actually showed some interest in her youngest sister, Princess Marina, for a spell -- but the liaison was quickly squashed by his mistress, Freda Dudley Ward.

Marina, too, had to settle for a modest consolation prize in the person of his youngest brother, the Duke of Kent -- who at one point was actually linked to Princess Ingrid of Sweden, the one who married the man originally engaged to Olga.

And Princess Elizabeth didn't have any more luck in sitting on a throne than her sisters: despite her ambitious mother pushing her on the then-Crown Prince (future King Umberto II) of Italy, nothing came of the matchmaking scheme. In the end she, too, had to settle for a modest match -- to Count Karl-Theodor of Törring-Jettenbach.

Nevertheless, the three sisters still managed to marry titled men -- which, considering what World War I had done to the European royal marriage market, wasn't too bad.