[citation needed] During his stay in Stockholm in 1802–1803, William's interest and rumoured affair with Aurora Wilhelmina Koskull attracted a lot of attention, and he reportedly had plans to marry her.

[4] On 25 August 1805, Prince William's father died, and he inherited the titles Duke of Gloucester and Edinburgh and Earl of Connaught.

[3] He was offered the throne of Sweden in 1812 by some members of the Swedish nobility, but the British government would not allow it;[citation needed] the French marshal Jean-Baptiste Bernadotte was eventually selected to become King Charles XIV John.

On the outbreak of war with France in 1793, Prince William was commissioned as a captain in the 1st Regiment of Foot Guards,[5] with the rank of lieutenant-colonel in the Army, backdated to March 1789.

[17][18] On 22 July 1816, Prince William married his first cousin Princess Mary, the fourth daughter of King George III.

[20] William was active in many walks of life, and on 27 April 1822 he chaired the first Annual General Meeting of London's new United University Club.

He did advocate the abolition of slavery, and he supported Caroline of Brunswick and Prince Augustus Frederick, Duke of Sussex, against King George IV.

[23] In a speech at the House of Lords on 5 February 1807, he stated that My lords, I cannot find language sufficiently strong to express my abhorrence and detestation of this abominable traffic in human blood; and I think the present question is the most momentous that ever came before your lordships: for what question can be more momentous, or come more closely home to our bosoms and our feelings of humanity, than that which concerns the welfare, the happiness, nay even the lives of myriads of our fellow creatures?

Because of the unequal character of his parents' marriage, the Duke was excluded from the House of Hanover, being considered only a British prince.

[31] William was granted use of his father's arms (being the arms of the kingdom, differenced by a label argent of five points, the centre bearing a fleur-de-lys azure, the other points each bearing a cross gules), the whole differenced by a label argent (or azure).