Another one who is old enough to remember the marriage, and agree with other older posters: it's not really that long ago and people weren't really that different then.
And that in a sense was the tragedy: Charles and his family still lived in the early 1900s, the rest of the nation had moved on. Nobody would have cared if he had married a slightly older woman with a normal healthy past. Which for most women at the time involved some experience of pre-marital sex.
On the other hand, when it became clear that he was basically taking advantage of the naivety of a young girl, that he married someone young enough to be his daughter precisely because he intended to lie to her - then people did care. That left a bad taste. Precisely because the 1980s were not the early 1900s.
Of course if Charles had had some basic personal integrity and the courage of his convictions, then that would also have been fine- he would have refused to behave like that even if he thought the nation might like it.
But failing personal integrity, some elementary understanding of the times he lived in might also have helped. We had sex in the 1980s. Men did not need to marry virgins. But men having mistresses had gone out of fashion a long, long time ago.
As for those who say this is fiction and the dialogue is made up, yes that's true, but that doesn't change the basic truth: that Charles chose an impressionable young girl because she would be easier to deceive.