Question: The younger brother, who became king, of Princess Mafalda of Savoy reigned for how many days?

Context:
Sen Soulintha
Sen Soulintha, Saen Surintha or Sen Sourintha (1511–1582) was born Chane Tian and became King of Lan Xang reigning 1571-1575 and again 1580-1582.
 Sen Soulintha was not of noble birth, rising from royal page to King Setthatirath’s Chief Minister.
 During the succession disputes in the Kingdom of Lan Na between King Setthatirath and King Mekuti, Sen Soulintha served Setthatirath as a general and successfully took several cities of Lan Na including Chiang Saen for which he was given the honorific name "Lusai" meaning “victory.”
 Sen Soulintha supported Setthatirath in leading the guerrilla campaigns during the Burmese invasions of King Bayinnaung.
 When Setthatirath died near Attapeu under suspicious circumstances in 1572, Sen Soulintha led the armies of Lan Xang back to Vientiane.
 A succession dispute erupted, which nearly led to civil war and provided a pretext for another Burmese invasion ordered by Bayinnaung and led by the Chief Minister Binnya Dala.
 Sen Soulintha defeated the Burmese and Lan Na forces led by Binnya Dala, an event which led to the latter’s exile, only to face a more massive invasion led by Bayinnaug the following year.
 Sen Soulintha again attempted to resort to guerilla tactics, but lacked popular support from his seizure of the throne.
 He and his son Ong Lo (Nakhon Noi) were captured by Bayinnaung and exiled to Pegu.
 The Burmese placed Setthathirath’s brother, and former "Ouphahat" or Viceroy, Prince Tha Heua on the throne.
 According to the Luang Prabang chronicles it was this brother, who had led a rebellion in Luang Prabang and tried to seize the throne from Setthathirath on the death of their father Photisarath.
 Prince Tha Heua took the regnal name Voravongsa and reigned under Burmese suzerainty from 1575-1579.
 Voravongsa was never popular, and drowned with his family while attempting to flee Vientiane in the face of popular uprising.
 In 1579, Bayinnaung dispatched a sizable army to restore order.
 According to Lao histories Sen Soulintha was then installed as king a second time in 1580.
 By that time Sen Soulintha was an old man and reigned only for two years before his son ascended the throne as Nakhon Noi and another succession dispute ensued.
Emperor Wenzong of Tang
Emperor Wenzong of Tang (809–840), personal name Li Ang, né Li Han (李涵), was an emperor of the Tang dynasty of China.
 He reigned from 827 to 840.
 Emperor Wenzong was the second son of Emperor Muzong and younger brother of Emperor Jingzong.
 A rare occurrence in Chinese history, Emperor Wenzong, along with his elder brother Emperor Jingzong and younger brother Emperor Wuzong, reigned in succession.
Umberto II of Italy
Umberto II (Italian: "Umberto Nicola Tommaso Giovanni Maria di Savoia" ; 15 September 190418 March 1983), was the last King of Italy.
 He reigned for 34 days, from 9 May 1946 to 12 June 1946, although he had been "de facto" head of state since 1944, and was nicknamed the May King (Italian: Re di Maggio ).
Louis Victor, Prince of Carignano
Louis Victor of Savoy (25 September 1721 – 16 December 1778) headed a French cadet branch of the Italian dynasty which reigned over the Kingdom of Sardinia, being known as the Prince of Carignano from 1741 till his death.
 Upon extinction of the senior line of the family, his great-grandson succeeded to the royal throne as King Charles Albert of Sardinia, while his great-great-grandson, Victor Emmanuel II, became King of Italy.
Marie Joséphine of Savoy
Marie Joséphine Louise of Savoy (Italian: "Maria Giuseppina Luigia" ; 2 September 1753 – 13 November 1810) was a Princess of France and Countess of Provence by marriage to the future King Louis XVIII of France.
 She was by Bourbon Royalists regarded as titular Queen of France from the death of her husband's nephew, the titular King Louis XVII of France in 1795, when her husband assumed the title of King, until her death, but in reality never had this title, as she died before he truly became King in 1814.
Princess Caroline Napoléon
Princess Caroline Marie Constance Napoléon (born 24 October 1980 in Paris) is a member of the House of Bonaparte, which reigned as Emperors of the French twice during the 19th century.
 She is the first child and eldest daughter of Prince Charles Napoléon and his first wife Princess Béatrice of Bourbon-Two Sicilies.
 Her younger brother is Jean-Christophe, Prince Napoléon, and younger half-sister is Princess Sophie Napoléon.
Princess Mafalda of Savoy
Princess Mafalda of Savoy (2 November 1902 – 27 August 1944) was the second daughter of King Victor Emmanuel III of Italy and his wife Elena of Montenegro.
 The future King Umberto II of Italy was her younger brother.
SS Principessa Mafalda
The SS Principessa Mafalda was an Italian transatlantic ocean liner built for the Navigazione Generale Italiana (NGI) company.
 Named after Princess Mafalda of Savoy, second daughter of King Victor Emmanuel III, the ship entered NGI's South American service between Genoa and Buenos Aires in 1909.
 At the time of her completion she was the largest Italian passenger ship afloat.
 The "Mafalda" was known for her luxury and was the preferred mode of travel for such celebrities of the day as Carlos Gardel.
Tupou VI
Tupou VI (ʻAhoʻeitu ʻUnuakiʻotonga Tukuʻaho; born 12 July 1959) is the King of Tonga.
 He is the younger brother and successor of the late King George Tupou V.
 He was officially confirmed by his brother on 27 September 2006 as the heir presumptive to the Throne of Tonga, as his brother (a bachelor) had no legitimate children.
 He served as Tonga's High Commissioner to Australia, and resided in Canberra until the death of King George Tupou V on 18 March 2012, when ʻAhoʻeitu ʻUnuakiʻotonga Tukuʻaho became King of Tonga, with the regnal name ʻAhoʻeitu Tupou VI.
Marie Jeanne Baptiste of Savoy-Nemours
Marie Jeanne of Savoy (Marie Jeanne Baptiste; 11 April 1644 – 15 March 1724) was born a Princess of Savoy and became the Duchess of Savoy by marriage.
 First married by proxy to Charles of Lorraine in 1662, Lorraine soon refused to recognise the union and it was annulled.
 She married Charles Emmanuel II, Duke of Savoy in 1665 who was her kinsman.
 The mother of the future Victor Amadeus II of Sardinia who saw the elevation of the House of Savoy to kings, she styled herself as Madama Reale or Madame Royale.
 She acted as Regent of Savoy from 1675 in the name of her son Victor Amadeus II, who was her husband's successor.
 Her regency officially ended in 1680, but she maintained power until her son banished her from further influence in the state in 1684.
 She left a considerable architectural legacy in Turin, and was responsible for the remodelling of the Palazzo Madama, which was her private residence.
 At the time of her death she was the mother of the King of Sardinia as well as great grandmother of two other kings, Louis I of Spain and Louis XV of France.

Answer: 34 days