If Princess Charlotte survived, there was no way Leopold would have been offered the Belgian Throne. It was not a matter of tolerance - the biggest and most influential party that backed Leopold’s candidacy during The National Congress of 1830 (when the future of Belgium was decided) was Britain. If Charlotte were still alive, Britain would certainly choose someone other than the spouse of the future Monarch of their country. Moreover, other countries, especially France and the Netherlands, would have never supported Leopold’s candidacy as it would mean too much British influence in Belgium: indeed, Leopold and Charlotte’s son would one day become King of both countries.
King George IV was always very fond of his son-in-law, even after Charlotte’s death: a token of the affection can be seen in the fact that King George (then Prince Regent) granted Prince Leopold the style of Royal Highness a year after Princess Charlotte’s death.
Although George IV died months before the National Congress started, his successor, King William IV, knew and appreciated Leopold as well: he was also well-aware of Leopold’s pro-British views and spirit, so his representatives actively supported Leopold’s candidacy.
It should be noted, however, that Britain was not the only major power that supported Leopold: Russia was also ‘fighting’ for Leopold’s case (who had ties with Russia, was a Lieutenant General in the Imperial Russian Army and had fought on the Russian side during Napoleon Russian Campaign), the Netherlands viewed Leopold as the most acceptable among the candidates (their candidate, Auguste de Beauharnais, 2nd Duke of Leuchtenberg, was deemed ‘unacceptable’ by both British and French), and even France withdrew its initial opposition and supported Leopold during the later stages of the Congress (it is often rumoured that this was done only after his engagement to Marie-Louise of France, the eldest daughter of King Louis-Philippe of France, was agreed on – even though Leopold was in a morganatic at the time).
