Queen Adelaide was dangerously ill in April 1837, at around the same time that she was present at her mother's deathbed in Meiningen, but she recovered. By June, it became evident that the King was fatally ill himself. Adelaide stayed beside William's deathbed devotedly, not going to bed herself for more than ten days. William IV died from heart failure in the early hours of the morning of 20 June 1837 at Windsor Castle, where he was buried. Victoria was proclaimed as queen, but subject to the rights of any issue that might be born to Adelaide on the remotely possible chance that she was pregnant.