During the exile of the royal family and after the Stuart Restoration in 1660, he was a member of the court of Charles II of England thanks to the influence of his powerful uncle, Henry Jermyn, 1st Earl of St Albans.

He remained loyal to James after the Glorious Revolution in 1688 and fought as a Jacobite during the Williamite War in Ireland, but in 1690 he pledged his loyalty to William and Mary.

Jermyn's father, an equerry to Charles I, supported the king during the Civil War and spent a period in exile during the Commonwealth of England.

Lord St Albans, who was secretary to the Queen Dowager until her death in 1669, obtained places at the exiled royal court for his nephews, Jermyn and his elder brother Thomas.

[3] According to rumour, his most notable conquest was Charles's widowed sister Mary of Orange, whom he met several times during the period of exile, and there were even stories that they were secretly married.

[8] Historians generally discount these rumours, but Charles II took them seriously, and reprimanded his sister for her lack of discretion, but with no effect: Mary sharply reminded her brother that his own love affairs hardly entitled him to judge her moral conduct.

Charles was especially angry because of the similar rumours that Jermyn's uncle Lord St Albans had secretly married the Queen Dowager.

[7][14] As a result, following the passing of the Test Act 1673, Jermyn was forced to resign his position in James' household and was granted a conciliatory pension of £500.

[2] Upon the accession of the Duke of York to the throne as James II on 6 February 1685, Jermyn remained one of his closest friends and advisors.

This group collectively influenced James to stay true to his Catholic faith in the face of growing criticism from parliament.

[2][21] However, rather than create a new corps of English Catholic army officers loyal to James, to help cover his gambling debts Dover sold half of the available commissions to refugee Huguenot gentlemen.

During the conflict, James despatched Dover on missions to Dublin, and on one occasion to France to petition Louis XIV for greater French assistance.

[1] A lieutenant-general in James' Jacobite army and commander of the Gards du Corps, Dover assured the Marquis de Louvois that the war in Ireland could be won with French support.

Having been appointed Intendant-General at Cork, he quarrelled with his former friend, the Duke of Lauzun, and James threw blame at Dover for the poor reception of French reinforcements which landed in Ireland in March 1690.

The French Marquis de Sourches expressed that Lord Dover should have been executed as a traitor for his "inexcusable incompetence and neglect of duty".

[1] Dover spent the rest of his life living quietly at his London townhouse or at his country estate at Cheveley Park.

[16] In accordance with his will, his body was moved to the English Convent and Friary of the Discalced Carmelites in Bruges, where he was buried in an elaborate Catholic ceremony on 24 May 1708.