Question: In which year was Emperor Akihito's eldest son's only daughter born?
Context: Aiko, Princess Toshi (敬宮愛子内親王 , Toshi-no-miya Aiko Naishinnō , born 1 December 2001) is the only child of Crown Prince Naruhito and Crown Princess Masako of Japan. The Brazilian Imperial Family is a royal family and cadet branch of the Portuguese Royal House of Braganza that ruled the Empire of Brazil for 67 years, between 1822 and 1889, after the proclamation of independence by Prince Pedro of Braganza who was later acclaimed as Pedro I, "Constitutional Emperor and Perpetual Defender of Brazil".  The members of the family are dynastic descendants of Emperor Pedro I. Claimants to headship of the post-monarchic Brazilian Imperial legacy descend from Emperor Pedro II, including the senior agnates of two branches of the House of Orléans-Braganza; the so-called "Petrópolis" and "Vassouras" lines.  Prince Pedro Carlos of Orléans-Braganza (born 1945) heads the "Petrópolis" line, while the "Vassouras" branch is led by his second cousin, Prince Luiz of Orléans-Braganza.  Rivalry within the family erupted in 1946 when "Dom" Pedro Gastão (1913–2007) repudiated the renunciation to the throne of his late father, Pedro de Alcântara, Prince of Grão-Pará (1875–1940), for himself and his future descendants, when he made a non-dynastic marriage in 1908.  Pedro de Alcântara was the eldest son of the Princess Imperial Isabel (1846–1921) who, as Pedro II's elder daughter and heir presumptive when he was dethroned, became the last undisputed head of the family after her father's death in exile in 1891.  Pedro Carlos is "Dom" Pedro Gastão's eldest son.  "Dom" Luiz descends from Isabel's younger son, Prince Luís (1878–1920) who, by a Bourbon princess, fathered Prince Pedro Henrique (1909–1981).  Dom Luiz is Pedro Henrique's son by a Bavarian princess and upholds his dynastic claim to the same legacy. Prince Tomohito of Mikasa (寛仁親王 , Tomohito Shinnō , 5 January 1946 – 6 June 2012) was a member of the Imperial House of Japan and the eldest son of Takahito, Prince Mikasa and Yuriko, Princess Mikasa.  He was a first cousin of Emperor Akihito, and was formerly sixth in the line of succession to the Japanese throne and the heir apparent to the princely house of Mikasa-no-miya and the title "Prince Mikasa".  Prince Tomohito was the first member of the Imperial House of Japan with a full beard since Emperor Meiji, thus earning him the popular nickname of the "Bearded Prince" (ヒゲの殿下 "Hige no Denka").  He died of cancer on 6 June 2012, aged 66. The Antrobus Baronetcy, of Antrobus in the County Palatine of Chester, is a title in the Baronetage of the United Kingdom.  It was created on 22 May 1815 for Edmund Antrobus, of Antrobus Hall, Antrobus, Cheshire, a Fellow of the Royal Society, with remainder to his nephews Edmund Antrobus and Gibbs Antrobus.  He died unmarried in 1826 and was succeeded according to the special remainder by his nephew Edmund, the second Baronet.  He and his brother Gibbs were the sons of John Antrobus, brother of the first Baronet.  The second Baronet was succeeded by his eldest son, the third Baronet.  He sat as Member of Parliament for Surrey East and Wilton.  His eldest son, the fourth Baronet, was a Colonel in the Coldstream Guards.  He died without surviving male issue and was succeeded by his younger brother, the fifth Baronet.  Most of the Amesbury Abbey estate in Wiltshire was sold the same year.  The fifth Baronet died unmarried and was succeeded by his first cousin, the sixth Baronet.  He was the son of Robert Crawfurd Antrobus, younger son of the second Baronet.  He was childless and on his death in 1968 the line of the second Baronet failed.  He was succeeded by his second cousin once removed, the seventh Baronet.  He was the eldest son of Edward Geoffrey Antrobus, second son of John Coutts Antrobus, son of the aforementioned Gibbs Antrobus, younger brother of the second Baronet.  As of 2008 the title is held by the seventh Baronet's eldest son, the eighth Baronet, who succeeded in 1995.  He lives in Johannesburg, South Africa. Takahito, Prince Mikasa (三笠宮崇仁親王 , Mikasa-no-miya Takahito Shinnō , 2 December 1915 – 27 October 2016) was a member of the Imperial House of Japan.  He was the fourth and youngest son of Emperor Taishō and Empress Teimei and was their last surviving child, the last surviving paternal uncle of Emperor Akihito.  His eldest brother was Emperor Shōwa (Hirohito).  After serving as a junior cavalry officer in the Japanese Imperial Army during World War II, the prince embarked upon a post-war career as a scholar and part-time lecturer in Middle Eastern studies and Semitic languages. Viscount Ullswater, of Campsea Ashe in the County of Suffolk, is a title in the Peerage of the United Kingdom.  It was created in 1921 for James Lowther upon his retirement as Speaker of the House of Commons.  He was the eldest son of the Hon. William Lowther, third son of the Hon. Henry Lowther, second son of William Lowther, 1st Earl of Lonsdale (see Earl of Lonsdale and Lowther Baronets for earlier history of the family).  The first Viscount lived to the age of 93, and was pre-deceased by both his eldest son the Hon. Christopher Lowther, a Conservative politician, and his eldest son's eldest son John Arthur Lowther (1910–1942) (who was Private Secretary to Prince George, Duke of Kent and was killed in the same air crash as him), the title being inherited by his seven-year-old great-grandson, the second and current Viscount, in an extremely rare instance of a great-grandson succeeding his great-grandfather in a peerage.  The second Viscount held office in the Conservative administrations of Margaret Thatcher and John Major and since 2003 he is one of the ninety elected hereditary peers that remain in the House of Lords after the passing of the House of Lords Act 1999.  As a descendant of the first Earl of Lonsdale he is also in remainder to this peerage and its subsidiary titles.  The current holder of the earldom, Hugh Lowther, 8th Earl of Lonsdale, is Lord Ullswater's fourth cousin. Shigeko Higashikuni (東久邇成子 , Higashikuni Shigeko , 6 December 1925 – 23 July 1961) , born Shigeko, Princess Teru (照宮成子内親王 , Teru-no-miya Shigeko Naishinnō ) , was the wife of Prince Morihiro Higashikuni and eldest daughter of Emperor Shōwa and Empress Kōjun.  She was the eldest sister to the present Emperor of Japan, Emperor Akihito. Prince Nobuhiko Higashikuni (b. 東久邇 信彦; 10 March 1945）is a Japanese aristocrat.  The eldest grandson of Emperor Hirohito, he is the eldest son of Shigeko, Princess Teru (the eldest daughter of Emperor Hirohito, and eldest sister of present Emperor Akihito) and Prince Morihiro Higashikuni, a grandson of Emperor Meiji.  He is nephew of reigning Emperor Akihito. Princess Mako of Akishino (眞子内親王 , Mako Naishinnō , born 23 October 1991) is the first child and oldest daughter of Fumihito, Prince Akishino and Kiko, Princess Akishino, and a member of the Japanese Imperial Family.  She is the eldest grandchild of Emperor Akihito and Empress Michiko. Masako, Crown Princess of Japan (皇太子徳仁親王妃雅子 , Kōtaishi Naruhito Shinnōhi Masako ) , born Masako Owada (小和田雅子 , "Owada Masako" ) on 9 December 1963, is the wife of Naruhito, Crown Prince of Japan, who is the eldest son of Emperor Akihito and Empress Michiko and the heir apparent to the Chrysanthemum Throne.  She is a member of the Imperial House of Japan through marriage.  Should the Crown Prince ascend the throne as expected upon his father's abdication, Masako will become empress consort.
Answer: 2001