Question: Who was the wife of the eldest son of the eldest grandchild of the British Queen Victoria?

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SS British Queen: British Queen was a British passenger liner that was the second steamship completed for the transatlantic route when she was commissioned in 1839.  She was the largest passenger ship in the world from 1839 to 1840.  She was named in honor of Queen Victoria and owned by the British and American Steam Navigation Company.  "British Queen" would have been the first transatlantic steamship had she not been delayed by 18 months because of the liquidation of the firm originally contracted to build her engine.

Dorothea von Salviati: Dorothea von Salviati (1907–1972), was the wife of Prince Wilhelm of Prussia, the eldest son of Crown Prince Wilhelm, the eldest son and heir of the last German Emperor, Wilhelm II.

Baron Monteagle of Brandon: Baron Monteagle of Brandon, in the County of Kerry, is a title in the Peerage of the United Kingdom.  Before he was deposed, James II had intended the title to be conferred upon one of his supporters, Stephen Rice.  Instead, it was created in 1839 in the reign of Queen Victoria for the Whig politician Thomas Spring Rice, a descendant of Stephen Rice.  He served as Chancellor of the Exchequer between 1835 and 1839.  He was succeeded by his grandson, the second Baron, his eldest son the Hon. Stephen Edmund Spring Rice having predeceased him.  The second Lord Monteagle was a unionist politician and was made a Knight of the Order of St Patrick in 1885.  On his death, the title passed to his son, the third Baron.  He held minor diplomatic office.  He was succeeded by his uncle, the fourth Baron.  He was the younger son of the aforementioned the Hon. Stephen Edmund Spring Rice, eldest son of the first Baron.  s of 2017 the title is held by the fourth Baron's great-grandson, the seventh Baron, who succeeded his father in 2013.

Prince Sigismund of Prussia (1864–1866): Prince Sigismund of Prussia (Franz Friedrich Sigismund; 15 September 1864 – 18 June 1866) was the fourth child and third son of Crown Prince Frederick William of Prussia (later King of Prussia and German Emperor as Frederick III), and Victoria, Princess Royal, eldest daughter of the British Queen Victoria.

Viscount Ullswater: 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.

Donatus, Landgrave of Hesse: Donatus, Prince and Landgrave of Hesse ("Heinrich Donatus Philipp Umberto"; born 17 October 1966) is the eldest son and successor of German aristocrat Moritz, Landgrave of Hesse, and his former wife, Princess Tatiana of Sayn-Wittgenstein-Berleburg.  A great-grandson of Victor Emmanuel III of Italy, he is named in part after Georg Donatus, Hereditary Grand Duke of Hesse.  He is also a great-great-great grandson of Queen Victoria of the United Kingdom, through his paternal grandfather Philipp's mother Margaret, a granddaughter of Queen Victoria.  His father Moritz was a third cousin of Queen Elizabeth II of the United Kingdom.

Antrobus baronets: 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.

Baron Addington: Baron Addington, of Addington in the County of Buckingham, is a title in the Peerage of the United Kingdom.  It was created on 22 July 1887 for the businessman and Conservative Member of Parliament, John Hubbard.  He was head of the firm of John Hubbard & Co and also sat as a Member of Parliament for Buckingham and the City of London.  His eldest son, the second Baron, was a partner in the family firm of John Hubbard & Co and represented Buckingham in the House of Commons as a Conservative.  He was succeeded by his eldest son, the third Baron.  He was three times Mayor of Buckingham.  On the death of his younger brother, the fourth Baron, the line of the eldest son of the first Baron failed.  The title passed to their first cousin once removed, the fifth Baron.  He was the grandson of Hon. Cecil John Hubbard, third son of the first Baron.  s of 2016 , the title is held by his eldest son, the sixth Baron.  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 of 1999.  Lord Addington sits on the Liberal Democrat benches.

Prince Joseph Wenzel of Liechtenstein: Prince Joseph Wenzel of Liechtenstein, Count Rietberg (German: "Joseph Wenzel Maximilian Maria von und zu Liechtenstein" ; born 24 May 1995) is the eldest child of Prince Alois of Liechtenstein, the Regent and Hereditary Prince of Liechtenstein, and his wife Princess Sophie of Bavaria, Duchess in Bavaria, he is also the eldest grandchild of the current ruling prince of Liechtenstein.

Wilhelm II, German Emperor: Wilhelm II or William II (German: "Friedrich Wilhelm Viktor Albert von Preußen", English: Frederick William Victor Albert of Prussia; 27 January 18594 June 1941) was the last German Emperor ("Kaiser") and King of Prussia, ruling the German Empire and the Kingdom of Prussia from 15 June 1888 to 9 November 1918.  He was the eldest grandchild of the British Queen Victoria and related to many monarchs and princes of Europe.

Supporting paragraphs: Dorothea von Salviati Wilhelm II, German Emperor
Answer: Dorothea von Salviati