He would have been like King Edward VIII of Great Britain, a bachelor who married after abdicating the throne ...

I meant to focus only on kings who never married ever in their lifetimes; but it seems that the discussion has extended to general situations where kings sat on thrones in an unmarried state ...

But a generalized discussion along these lines would basically be comparable to the post -- which I brought up some time ago -- on kingdoms which underwent periods without queens. As it was, Bavaria had only one queen from 1854 (the death of Therese, consort of King Ludwig I) and the death in 1889 of Marie (consort, later widow, of King Maximilian II, and mother of Kings Ludwig II and Otto).

Things could have been different, had Ludwig II married Duchess Sophie Charlotte in Bavaria and Otto married Princess Theresa of Bavaria, as hoped and expected ...

The next queen would be the last: Maria Theresia, whose husband in 1913 became the self-proclaimed King Ludwig III. According to witnesses, she did not especially exult over her newly exalted status, since his cousin was still living at the time. If anything, her expression was muted (you could see it in her eyes) -- indicating her grave reservations over his actions in deposing Otto (who died three years later). She must have had a strong sense of legitimacy.

That being said, even before she was proclaimed queen, Maria Theresia may have been the de facto first lady of Bavaria, after the death of Marie ...