On 9 November 1905, King Edward VII declared his eldest daughter Princess Royal.
He further ordered Garter King of Arms to gazette Lady Alexandra Duff and her sister Lady Maud Duff with the style and attribute of Highness and the style of Princess prefixed to their respective Christian names, with precedence immediately after all members of the British Royal Family bearing the style of Royal Highness.
From that point, Her Highness Princess Alexandra held her title and rank, not from her ducal father, but from the decree issued by will of the sovereign (her grandfather).

Around 1910, Alexandra became secretly engaged to Prince Christopher of Greece and Denmark, a son of King George I of the Hellenes.
The engagement was terminated when their disapproving parents learned of the liaison.
On 9 November 1905, King Edward VII declared his eldest daughter Princess Royal. He further ordered Garter King of Arms to gazette Lady Alexandra Duff and her sister Lady Maud Duff with the style and attribute of Highness and the style of Princess prefixed to their respective Christian names, with precedence immediately after all members of the British Royal Family bearing the style of Royal Highness. From that point, Her Highness Princess Alexandra held her title and rank, not from her ducal father, but from the decree issued by will of the sovereign (her grandfather).
Around 1910, Alexandra became secretly engaged to Prince Christopher of Greece and Denmark, a son of King George I of the Hellenes. The engagement was terminated when their disapproving parents learned of the liaison.
Princess Alexandra, 2nd Duchess of Fife