Surfing in the Internet I suddenly found this site:
http://www.heraldica.org/topics/national/monaco.htm and was surprised to read some interesting words there. It seems the history is always repeated and all Alberts of this family are doomed to be unmarried...The same names...the similar situations...
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The Succession Crisis
One of the motivations for the treaty was an impending succession crisis.
In 1918 the reigning prince was Albert I, only child of Charles III. Albert's only child Louis (1870-1949) remained unmarried, and the next of kin was Albert's first cousin Wilhelm duke of Urach (1864-1928), a German national (although born and raised in Monaco), son of Albert's aunt Florestine. It seemed possible that Monaco would pass into German hands, and France could not accept that. Already, steps had been taken in Monaco. Louis, while serving in the French army in Algeria, befriended the laundress of his regiment, who later asked him to look after her daughter in Paris, Marie Juliette Louvet. He looked so closely after her that he sired a daughter, Charlotte-Louise-Juliette (30 Sep 1898-15 Nov 1977), and had recognized her as his child in 1900 in Constantine. An ordinance of May 15, 1911 acknowledged and approved her recognition as child of Louis, and admitted her in the sovereign family, but in violation of the statutes of 1882; the ordinance was invalid, as the National Council pointed out to the prince in 1918. As a consequence, an ordinance of October 30, 1918 modified the Statutes to allow the Prince or, with the Prince's consent, the Hereditary Prince, in the absence of legitimate issue of his own, to adopt a child in or outside of the family. The adopted child fully inherits all the rights, titles and prerogatives of the Prince who adopted him or her, including succession rights to the crown. Should the prince have legitimate issue after the adoption, the adopted child takes rank after the legitimate issue. Another ordinance of October 31 stated the conditions for an adoption, including that the child be 18 years of age; and that adoption took effect immediately.
Subsequently Charlotte, was adopted by Louis in Paris, at the Monegasque embassy, on May 16, 1919, in the presence of the French president and foreign affairs minister, Albert, Louis, the president of the Monegasque national council and the mayor of Monaco. There is a shadow of a doubt on the legality of the adoption. The Monegasque civil code (arts. 240 and 243) require that the adopting party be at least 50 and the adoptee 21. The 1918 ordinance changed the age limit to 18 (Charlotte was 20 at the time of adoption) but not the other age limit, and Louis was 48 at the time.
Charlotte was titled duchesse de Valentinois by Albert I on May 20, 1919 and heir apparent on August 1, 1922 after Louis II's accession on June 22. On March 19, 1920 she married the comte Pierre de Polignac (1895-1964, divorced 1933), a member of a junior branch of the Polignac family. An ordinance of February 29 had given him Monegasque nationality, and an ordinance of March 18 had changed his name and arms to those of Grimaldi; on March 20, he was allowed to take the title of duc de Valentinois. Charlotte and Pierre Grimaldi had a daughter Antoinette, baronne de Massy (b. 28 Dec 1920) and a son Rainier (b. 31 May 1923). By a declaration of May 30, 1944 in Paris, Charlotte ceded her rights to Rainier (with a reservation if he should predecease), and Rainier accepted in Paris on June 1. An ordinance of June 2 1944 acknowledged and confirmed the Prince's assent to those declarations, and Rainier was made Hereditary Prince. When to the Journal de Monaco published the ordinance on 22 June 1944, it added: "His Excellency the comte de Maleville, minister of Monaco in France, has been asked to inform the French government of this event, pursuant to the clauses of the treaty of 17 July 1918."
Louis II died on May 9, 1949. In the absence of any male heir to the Goyon-Matignon family, the titles of Valentinois and Estouteville became extinct in French law. The principality of Monaco passed to Rainier III. Before Rainier married Grace Kelly in April 1956, he notified the French government of his plans; the French ministry of Foreign affairs replied with a message of congratulations, thus establishing the requisite "prior understanding". (Cited in Gallois 1964, 107)."