Prince Aage, Count of Rosenborg (Aage Christian Alexander Robert; June 10, 1887 – February 19, 1940), was a Danish prince and officer of the French Foreign Legion. He was born in Copenhagen the eldest child and son of Prince Valdemar of Denmark and Princess Marie d'Orléans.

Prince Aage carried on a passionate flirtation with Princess Marie Bonaparte, the wife of his cousin Prince George of Greece and Denmark, who had also enjoyed intimacies with his father. In neither case does it appear that Prince George objected, or felt obliged to give the matter any attention. In 1909 Prince Aage joined the Danish Army, and by 1913 had risen to the rank of lieutenant. During World War I he served as an observer in Italy for a year. Returning home to Denmark he was promoted to captain.

Without the legally required permission of the Danish king, Aage married Matilda Calvi dei conti di Bergolo (Buenos Aires, 17 September 1885 – Copenhagen, 16 October 1949), daughter of Carlo Giorgio Lorenzo Calvi, 5th Count di Bergolo by his wife Baroness Anna Guidobono Calvalchini Roero San Severino, in Turin on 1 February 1914. A few days later, he renounced his place in the line of succession to the Danish throne, forfeiting his title of Prince of Denmark, and his style of Royal Highness. With the king's authorisation, he assumed the title "Prince Aage, Greve af (Count of) Rosenborg" and the style of Highness on 5 February 1914. Although the comital title in the Danish nobility was made hereditary for all of his legitimate descendants in the male line, use of the princely prefix was restricted to himself and his wife alone. Aage and Mathilde had one son before their divorce in 1939:

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