[3] Alleyne was fifth and youngest son of William Fitzherbert of Tissington in Derbyshire, who married Mary, eldest daughter of Littleton Poyntz Meynell of Bradley, near Ashbourne.

[1] His father, who was Member for the Borough of Derby and a Commissioner of the Board of Trade, committed suicide on 2 January 1772 due to pecuniary trouble.

The peace with the American colonies, which was agreed to at about the same date, was not brought to a conclusion under Fitzherbert's charge, but he claimed to have taken a leading share in the previous negotiations which rendered it possible.

This successful diplomacy led to his promotion in the summer of 1783 to the post of envoy extraordinary to the Empress Catherine of Russia, and he accompanied her in her tour round the Crimea in 1787.

[1][5] When differences broke out between Great Britain and Spain respecting the right of British subjects to trade at Nootka Sound and to carry on the southern whale fishery, he was despatched to Madrid (May 1791) as ambassador extraordinary, and under his care all disputes were settled in the succeeding October, for which services he was raised to the Irish peerage with the title of Baron St.

[1][6] In the following year, Commander George Vancouver and the officers of HMS Discovery made the Europeans' first recorded sighting of Mount St. Helens on 19 May 1792, while surveying the northern Pacific Ocean coast.

A treaty of alliance between Great Britain and Spain was concluded by him in 1793, but as the climate of that country did not agree with his health he returned home early in 1794.

Very shortly after his landing in England, St. Helens was appointed to the ambassadorship at the Hague (25 March 1794), where he remained until the French conquered the country, when the danger of his situation caused much anxiety to his friends.

The terms of the agreement were quickly settled, and on its completion he was promoted to the peerage of the United Kingdom as Baron St. Helen's, in the Isle of Wight and County of Southampton.

When Addington was forced to resign the premiership, St. Helens, who was much attached to George III, and was admitted to more intimate friendship with that king and his wife than any other of the courtiers, was created a lord of the bedchamber (May 1804), and the appointment is said to have been made against Pitt's wishes.

She referred to him as, "a dear and valuable saint," and said of him in a letter to her companion Lady Harcourt, "There is no man I love so well, and his tenderness to me has never varied, and that is a thing I never forget."