The Last Rebel, The Last Battle

As the latest biography of James, the Duke of Monmouth notes:

At first light on July 6, 1685, the last battle ever fought on English soil was almost over. On one side of the watery pasture at Sedgemoor was the dashing thirty-six-year-old Duke of Monmouth, the charismatic son of Charles II, adored by the people. A reformer, a romantic, and a Protestant, he was fighting the army he had once commanded, in opposition to his uncle, King James II. Yet even before he launched his attack, Monmouth knew he would die.

How did he know that he would die? Because he was trapped and his surprise attack had failed, according to this UK Battlefields Resource Center post:

During the night, in a last desperate attempt to salvage something from his abortive rebellion, Monmouth launched a surprise night attack from the least expected direction, across the marshy wastes of Sedgemoor. But the rebels’ bold strategy was discovered before they reached the royal camp and then, in the darkness, their cavalry failed to locate the ford giving access to the royal camp.

With the element of surprise lost any chance of victory had disappeared. The rebel horse soon fled the field and in open country without cavalry support Monmouth’s infantry proved an easy target for the royal cavalry. The discipline, experience and firepower of the well equipped professional soldiers of the army of James II soon began to tell. As the morning light revealed the rebels’ true plight of the rebels, Feversham launched a join cavalry and infantry attack. Monmouth’s army was totally destroyed.

Monmouth, aka James Monmouth Scott, was Charles II's favorite bastard:

Born in the backstreets of Rotterdam in the year his grandfather Charles I was executed, Monmouth was the child of a turbulent age. His mother, the first of Charles II's famous liaisons, played courtesan to the band of raw and restless young royalists forced abroad by the changing political current. Conceived during a revolution and born into a republic, Monmouth, by the time he was twelve, was the sensation of the most licentious and libertine court in Europe. Adored by the king and drenched in honors, he became the greatest rake and reprobate of the age.

On his path to becoming "the last royal rebel," Monmouth consorted with a spectacular list of contemporaries: Louis XIV was his mentor, William of Orange his confidant, Nell Gwyn his friend, the future Duke of Marlborough his pupil, D'Artagnan his lieutenant, John Dryden his censor, and John Locke his comrade. Anna Keay expertly chronicles Monmouth's life and offers splendid insight into this crucial and dramatic period in English history.

It's interesting to note that another of Charles II's illegitimate sons fought for James II: Henry Fitzroy, the 1st Duke of Grafton. He was one of Charles's three sons with Barbara Palmer, the 1st Duchess of Cleveland. He would later support William of Orange in his invasion of England to depose James II, leaving his uncle's service with John Churchill. Churchill and Louis de Duras, 2nd Earl of Feversham also led the king's army against Monmouth's troops. Fitzroy was a Catholic; Monmouth an Anglican.

Monmouth's army was also commanded by Ford Grey, 1st Earl of Tankerville and Benjamin Hewling. Tankerville survived after the defeat:

He was in command of the cavalry, and its defeat on two occasions may have been caused by his cowardice, possibly even by his treachery. He was taken prisoner and condemned for high treason, but he obtained a pardon by freely giving evidence against his former associates, and was restored to his honours in June 1686.

Hewling was one of those executed in the Bloody Assizes condemned by Lord Chief Justice George Jeffreys, who had also presided over many of the Popish Plot trials. Just to show how tangled these webs of family, rebellion, and treachery were: Henry Fitzroy's guardian, Roger Palmer, Barbara's husband and a prominent Catholic (she had become Catholic too) was accused of involvement in the Popish Plot. He was imprisoned in the Tower of London but defended himself ably against Jeffreys and the Lord Chief Justice at the time, William Scroggs.

Monmouth was executed soon after his defeat, on July 15, 1685, despite offering to convert to Catholicism--at the same time, being refused Communion in the Church of England by the bishops of Bath and Wells (Thomas Ken, later a nonjuror) and Ely (Francis Turner, ditto) because he would acknowledge his sins. His execution, commuted from the usual penalty of being hanged, drawn, and quartered, was not merciful at all because Jack Ketch, the headsman, could not cut off the poor man's dead efficiently or expeditiously. According to Thomas Macaulay, Monmouth feared it would be so:

He then accosted John Ketch the executioner, a wretch who had butchered many brave and noble victims, and whose name has, during a century and a half, been vulgarly given to all who have succeeded him in his odious office. 'Here ', said the Duke, 'are six guineas for you. Do not hack me as you did my Lord Russell. I have heard that you struck him three or four times. My servant will give you some more gold if you do the work well.' He then undressed, felt the edge of the axe, expressed some fear that it was not sharp enough, and laid his head on the block. The divines in the meantime continued to ejaculate with great energy; 'God accept your repentance! God accept your imperfect repentance!'

The hangman addressed himself to his office. But he had been disconcerted by what the Duke had said. The first blow inflicted only a slight wound. The Duke struggled, rose from the block, and looked reproachfully at the executioner. The head sank down once more. The stroke was repeated again and again; but still the neck was not severed, and the body continued to move. Yells of rage and horror rose from the crowd. Ketch flung down the axe with a curse. 'I cannot do it,' he said; `my heart fails me.' 'Take up the axe, man,' cried the sheriff. 'Fling him over the rails,' roared the mob. At length the axe was taken up. Two more blows extinguished the last remains of life; but a knife was used to separate the head from the shoulders. The crowd was wrought up to such an ecstasy of rage that the executioner was in danger of being torn in pieces, and was conveyed away under a strong guard.

Finally, you might recall that Raphael Sabatini wrote Captain Blood, an historical novel about a doctor, Peter Blood, who treats a Monmouth supporter wounded at the Battle of Sedgemoor and is transported to the West Indies as a slave during the Bloody Assizes. The novel was made into a movie in 1935 with Errol Flynn and Olivia de Havilland--Vernon Steele appears as James II and Leonard Mudie as Justice Jeffreys. TCM.com provides some scenes from the movie--at the beginning his servant tells Blood that he is thought to be a Papist by some because he is not fighting for Monmouth!