Ulrika Eleonora, Queen of Sweden abdicates in favour of her husband, who becomes King Frederick I on March 24.

Ulrika Eleonora or Ulrica Eleanor, also known as Ulrika Eleonora the Younger, was Queen of Sweden from 5 December 1718 until her abdication on 29 February 1720 in favour of Frederick, her husband. Upon his accession, as King Frederick I, she served as his queen consort until her death on 24 November 1741.

Frederick I was King of Sweden from 1720 until his death, having been prince consort of Sweden from 1718 to 1720, and was also Landgrave of Hesse-Kassel from 1730. He ascended the throne following the death of his brother-in-law absolutist Charles XII in the Great Northern War, and the abdication of his wife, Charles's sister and successor Ulrika Eleonora, after she had to relinquish most powers to the Riksdag of the Estates and thus chose to abdicate. His powerless reign and lack of legitimate heirs of his own saw his family's elimination from the line of succession after the parliamentary government dominated by pro-revanchist Hat Party politicians ventured into a war with Russia, which ended in defeat and the Russian tsarina Elizabeth getting Adolf Frederick of Holstein-Gottorp instated following the death of the king. Whilst being the only Swedish monarch called Frederick, he was Frederick I of Hesse-Kassel and thus Frederick I also of Sweden, though other Swedish monarchs with non-repeating names had not been enumerated.

February 29 is a leap day —an intercalary date added periodically to create leap years in the Julian and Gregorian calendars. It is the 60th day of a leap year in both Julian and Gregorian calendars, and 306 days remain until the end of the leap year. It is the last day of February in leap years only. It is also the last day of meteorological winter in the Northern Hemisphere and the last day of meteorological summer in the Southern Hemisphere in leap years.