, by
Nicaise de Keyser, 1846 He entered the
British Army, and in 1811, as a 19-year-old
aide-de-camp in the headquarters of
Arthur Wellesley, 1st Duke of Wellington, was allowed to observe several of Wellington's campaigns of the
Peninsular War. Though not yet 20, the young prince, according to the customs of the time, was made
lieutenant colonel on 11 June 1811 and
colonel on 21 October that year. He took part in the
Siege of Badajoz and the
Battle of Salamanca in Spain in 1812. Later that year, on 8 September, he was made an
aide-de-camp to the
Prince Regent and on 14 December 1813 promoted to
major-general. His courage and good nature made him very popular with the British, who nicknamed him "Slender Billy". He returned to the
Netherlands in 1813 when his father became sovereign prince, and in May 1814 succeeded Sir
Thomas Graham as the highest-ranking officer of the British forces stationed there. On 8 July 1814, he was promoted to
lieutenant-general in the British Army, and on 25 July to
general. As such, he was senior officer of the Allied army in the
Low Countries when
Napoleon I of France escaped from
Elba in 1815. He relinquished command on the arrival of the Duke of Wellington, and, though this was his first real battle, served as commander of the
I Allied Corps, first at the
Battle of Quatre Bras (16 June 1815) and then at the
Battle of Waterloo (18 June 1815), where he was wounded in his left shoulder by a musket ball. He was aged 22. As a sign of gratitude for what the Dutch throne styled "his" victory at Waterloo, William was offered
Soestdijk Palace by the Dutch people. Military historian
William Siborne blamed many casualties suffered by Coalition forces during the
Waterloo campaign to William's inexperience. In response, Siborne was accused by Lieutenant-General
Willem Jan Knoop of misrepresenting William's actions at Waterloo. An inspection into the archives of Siborne by Dutch officer
Francois de Bas in 1897 claimed to discover the "selective use of sources" and "numerous miscounts and untruths". == Marriage ==