Count Antoine Seilern (17 September 1901 – 6 July 1978) was an Anglo-Austrian art collector and art historian. He was considered, along with Sir Denis Mahon, to be one of a handful of important collectors who was also a respected scholar. The bulk of his collection was bequeathed anonymously to the Courtauld Institute of Art. Known as the "Princes Gate bequest", most of it is on display at the Courtauld Gallery in London.

Count Antoine Edward Seilern und Aspang was born on 17 September 1901 at Frensham Place, Farnham, in Surrey, England. He was the youngest of the three sons of Count Carl Seilern und Aspang (1866–1940) and the American heiress Antoinette "Nettie" née Woerishoffer (1875–1901). He therefore enjoyed citizenship of both Austria and the United Kingdom. His ancestors had been ennobled after successful involvement with the Pragmatic Sanction of 1713. His father's sister Ida was married to Phillip Hennessy, whose sister Nora was the wife of the Royal Academician Lord Methuen.

He had two older brothers, Count Charles Hugo ("Chappie"), born 1899, and Count Oswald Seilern, born 1900. His mother died five days after he was born. Thereafter the three Seilern boys divided their time between their grandmother, Anna Woerishoffer, in New York City, and their father in London and Vienna, in the company of nannies and governesses (and frequently chaperoned by the Swiss-born American artist Adolfo Müller-Ury), though until America entered the First World War Mrs Woerishoffer spent 1912 to 1916 with her grandsons in Vienna. Anna Woerishoffer's wealth derived mainly from the German-language New York newspaper, the Neue-Yorker Staats-Zeitung, and her late husband's success on Wall Street. Seilern, like his older brothers, grew up with a passion for horse-racing and shooting.

After the First World War Seilern relinquished his Austrian citizenship. However, despite this, he graduated in 1920 from the Realgymnasium in Vienna before attending the Wiener Handelsakademie (1920–1921) and then, at the start of 1922, he enrolled at the Technische Hochschule in order to study for an engineering certificate until 1924. He then worked briefly for a Yugoslavian lumber company, and in Vienna in finance.

A friend in Vienna, the old Count Karol Lanckoroński (Karl Lanckoronski) a large man of huge charm, who had a fine collection of art at his palace in Vienna, persuaded Seilern he should collect also, and in 1931, after the death of his grandmother, when he received his share of an enormous inheritance, he was able to devote himself to the study of art history and to serious collecting. During the years 1930 to 1933 he travelled widely, particularly in Africa, in search of big-game (as the trophies that could be seen at his house at Princes Gate after the war testified) though his bags were reputedly always packed with art books. He even acquired a pilot's license in Berlin.

However, in 1933, Count Karl Wilczek, another family friend who was also an art historian, recommended Seilern take private lessons with the great Hungarian art historian Johannes Wilde, very soon a mentor who was to become a lifelong friend. Seilern shortly afterwards enrolled at Vienna University to study the history of art with Karl Maria Swoboda, Julius Schlosser and Hans Sedlmayr. Unusually, perhaps, his subsidiary subject at university was Kinderpsychologie (Child Psychology), taught by a lady who was a pupil of Sigmund Freud and who was vouched for by his friend Jan van Gelder. Seilern wrote his doctoral dissertation on the Venetian influences on the ceiling paintings of Sir Peter Paul Rubens (Die venezianischen Voraussetzungen der Deckenmalerei des Peter Paul Rubens) which he completed in 1939. Rubens remained a lifelong passion and he later remarked, "Everything connected with Rubens interests me."

Meanwhile, Seilern had started to collect seriously, and was being advised by Wilde, and Ludwig Burchard, the great Rubens scholar. His collection of Rubens' paintings would soon include Landscape by Moonlight (which was once the possession of Sir Joshua Reynolds), and large numbers of paintings, drawings, copies and modelli also by Rubens, as well as oil sketches by Tiepolo and other masters. Between the wars and whilst studying in Vienna he had kept his art collection in an apartment at Brahmsplatz 1.

At the annexation of Austria by Nazi Germany in 1938, and because of his British citizenship (he had apparently hung the Union Jack from his house in Vienna), Seilern decided in 1939 to return to England, bringing with him his already large art collection and his library. Based in England now he was able to provide finance to support to another art historian fleeing from Nazi-occupied Austria, Ludwig Münz, as well as helping Johannes Wilde and his Jewish wife to leave Vienna. The Director of the National Gallery, Sir Kenneth Clark, sponsored Wilde who was reunited with Seilern at Aberystwyth in Wales where his collection was important enough to be hidden with works of art from the National Gallery and Royal Collection. Seilern then enlisted in the ranks of the British Army (though aged thirty-eight), serving in the Royal Artillery, and in 1940 immediately volunteered for the disastrous Russo-Finnish campaign, only escaping from occupied Norway. It was at the end of the Second World War, whilst acting as a German interpreter in the Intelligence Corps, that he appeared at the door of Professor Jan van Gelder in Amsterdam to pick up three oil sketches by Rubens he had bought for Seilern from the Koenig collection in 1940 and had deposited as 'Swedish property' at an Amsterdam bank.