The Braganšas had three dethroned kings.
D.Afonso VI, dethroned by his brother Infante D.Pedro.
D.Afonso's wife, Maria Francisca of Savoy divorced him and immediately remmaried her brother-in-law D.Pedro who retained the title of Regent as long as D.Afonso lived.
However, Maria Francisca always retained the title and honours of Queen, a condition she only regained when D.Afonso died and D.Pedro ascended to the throne as king D.Pedro II.
Once a queen, always a queen.
D.Miguel I married Pss Adelheid of Loewenstein-Wertheim-Rosenberg after being deposed.
Pss Adelheid assumed the title of Queen afyter marryin the king.
Identicall situation for Pss Augusta-Victoria of Hohenzollern-Sigmaringen who married king D.Manuel II after he lost his throne and even so assumed the title of Queen.
Is it a general principle that the wife of a once-enthroned king is acknowledged as queen? The reason for my asking is the cases of Alexandra of Yugoslavia (consort of King Peter II), Anne of Romania (consort of King Michael), and Margarita of the Bulgarians (consort of King Simeon). By contrast, Crown Princess Katherine of Serbia today (like her husband's first wife) does not enjoy this honor.
A living king may be dethroned for a number of reasons -- e.g. abdication (whether forced, e.g. Ludwig I of Bavaria, or voluntary, e.g. Edward VIII of Great Britain), deposition (e.g. James VII/II of Great Britain, Louis-Philippe of the French), the abolition of the monarchy (e.g. Constantine II of the Hellenes).
But as a general rule, he retains the title of KING, with the qualification of Majesty; it's just that he ceases to be THE King of __. An exception would be Edward VIII of Great Britain, who adopted the more modest title of Duke of Windsor, with the qualification of Royal Highness. It has been explained that this was in anticipation of his marriage to Wallis Warfield Simpson, who (under English common law) would have been styled Queen (with the qualification of Majesty), had he continued styling himself as King. It's just that he knew the public at large would never accept this. Hence, the lower title with qualifier. Still, he hoped that his wife, who would legally become the Duchess of Windsor, would at least enjoy the qualification of Royal Highness. Indeed, she would have -- but for the Letters Patent issued in 1937: that's what it took, to deny her the three letters.
In present times, it has been stated that Camilla would normally become legally queen, once her husband succeeds to the British throne as king: this would be the default assumption, unless measures are taken to prevent this. As it was, an understanding and agreement was reached before marriage, that she would style herself as HRH The Duchess of Cornwall, during the remaining years of her husband was the Prince of Wales, and then afterward HRH The Princess Consort. But for the said measures, she WOULD legally become queen, once her husband becomes king. And there would be nothing to stop her from styling herself as The Princess of Wales.
Anyhow, getting back to the subject of continental European royalty: it has been asserted that HSH Princess Hermine Reuss of Greiz, who became the second wife of Kaiser Wilhelm of Germany, was universally acknowledged as "Empress Hermine" and addressed as "Your Imperial Majesty", despite the fact that the German monarchy by then had been abolished. Is this true? In this, her situation would perhaps be comparable to that of the other royal women who married once-enthroned kings after the monarchies got abolished ...
If the widowed King Ludwig I of Bavaria had remarried, after the death in 1854 of his wife (born Princess Therese of Saxe-Hildburghausen), would his wife have been styled as Queen, with the qualification of Majesty? I would assume so -- as long as she was of *equal* birth (in accordance with the dynastic requirements of the Wittelsbach house laws). It's just that she obviously would not have been Her Majesty THE Queen of Bavaria: that distinction belonged to Marie, consort of King Maximilian II (who had succeeded to the throne upon his father's abdication in 1848).
I know that both Leopold III of the Belgians and Carol II of Romania retained the title of King, despite abdicating or being deposed. It's just that neither second wife of either was ever styled with the title of Queen. So Wallis was actually in good company, insofar as she was not the only person thus denied. It's just that she didn't even get the qualification of HRH, as the other women did, and which Camilla today enjoys.