Prince Felix of Bourbon-Parma was the son of the last Duke of Parma, Robert I 1848-1907 and his second wife, Infanta Maria Antonia of Portugal 1862-1959, and the brother of Zita, the last Empress of Austria and Queen of Hungary.
Prince Felix joined the Austrian Dragoon Regiment No. 15 as a war volunteer in autumn 1914, where he advanced to the rank of First Lieutenant. He was much mentioned in Nov. 1917, when he saved his brother-in-law, Emperor Charles of Austria-Hungary, from drowning in the Isonzo.
During the war in October 1918 he became engaged to the future Grand Duchess Charlotte of Luxembourg, the next eldest sister of the Grand Duchess Maria-Adelheid of Luxembourg, born on 23 January 1896. A sapphire and diamond engagement ring made in platinum, was presented to Charlotte, see above.
Prince Felix married the Grand Duchess, who was his cousin, in Luxembourg Cathedral on 6 November 1919.
The wedding present of her husband is worn by the Grand Duchess Charlotte, as bridal jewelry, see above in the picture on the left, it is from the former property of Empress Zita of Habsburg-Lorraine>>, who sold it to her brother in exile.
The whereabouts of the imperial diamond necklace after the abdication of Grand Duchess Charlotte in 1964 in favour of her son Jean, is unknown.
Possibly the jewellery was given to one of your children:
Jean Benoît Guillaume Robert Antoine Louis Marie Adolphe Marc d'Aviano (1921-2019) oo Princess Joséphine Charlotte of Belgium
Élisabeth Hilda Zita Marie Anna Antoinette Friederike Wilhelmine Louise (1922-2011) oo Franz Ferdinand Hohenberg (son of Maximilian Hohenberg, grandson of Franz Ferdinand of Austria-Este)
Marie-Adélaïde Louise Thérèse Wilhelmine (1924-2007) oo 1958 with Carl Joseph Count Henckel von Donnersmarck (grandson of Count Edwin Henckel von Donnersmarck)
Marie Gabrielle Aldegunde Wilhelmine Louise (* 1925) oo Knud Count of Holstein-Ledreborg
Charles Frédéric Louis Guillaume Marie (1927-1977) oo Joan Douglas-Dillon, daughter of C. Douglas Dillon
Alix Marie Anne Antoinette Charlotte Gabrielle (1929-2019) oo Prince Antoine of Ligne
Grand Duchess Maria Anna of Luxembourg, Princess of Braganca, at the top left of the picture, the mother of Grand Duchess Charlotte wore the Emperor's Diamond Diadem of Zita on the occasion of her daughter's wedding in November, 1919, to Prince Felix of Bourbon-Parma, brother of Zita.
At the same event, on the right side of the picture, the Maria-Antonia Duchess of Parma with the pearl Collier de Chien, of her daughter Empress Zita, can be recognized, possibly also the diamond riviers of her. The Collier de Chien and the diamond tiara of the Emperor is now in the possession of the Habsburg family, Regina of Habsburg wore it on her wedding day. Archduchess Francesca of Habsburg was pictured with the Chollier de Chien.