I’m not sure I believe Andrew and Koo were ever that serious.
But yes, what I recall reading is the general accepted idea that the future King of England was told early in his romance that he could not marry a woman who was already “used goods”. The Palace brass were horrified until their stiff upper lips quivered that some tabloid might someday publish a “What it’s Like to Sleep With the Queen” article. Two decades onward, after all that transpired, apparently nobody gives a flying hoot.
Of course the deciding factor with Diana was apparently that she was still intacta, with no past baggage to detract from her character.