Buckingham (Sheffield) Dukes--

John Sheffield
1st Duke of Buckingham

@Wikipedia

John Sheffield

(1647-1721)

1st Duke of Buckingham

1703-1721

Son of: Edmund and Elizabeth (Cranfield)

John Sheffield (1648-1721), son of Edmund and Elizabeth (Cranfield), succeeded as third Earl of Mulgrave at the age of ten. In 1666 he was a volunteer with Prince Rupert in the Fleet. On June 13, 1667, he was commissioned captain of a troop of horse. In February, 1673, he became Gentleman of the Bedchamber to King Charles II. In the summer of 1673 he commanded a war ship, The Royal Katherine. In December he was commissioned colonel of the 'Old Holland' regiment of foot. On April 23, 1674, probably by the influence of his then mistress, the Duchess of Cleveland, he was elected a Knight of the Garter. A haughty, arrogant young man, Mulgrave made many enemies, and in his early years he was involved in a number of quarrels. In 1669 King Charles stopped a duel between Mulgrave and the Earl of Rochester. In July 1670, the King, 'having timely notice,' prevented a duel between Mulgrave and Mr. Digby, second son to the Earl of Bristol. . . On October 3, 1671, a writer reported that 'Lord Mulgrave has been wounded in a duel with Mr. Felton' . . In June, 1675, Captain Percy Kirke accused Mulgrave of fathering his sister's stillborn child, fought with him and 'worsted and wounded him' . . . . (Court Satires of the Restoration: 269)

Husband of:
1. Ursula Stawell (d.1697)  mar 1685
2. Catherine Greville (d.1703) mar 1698
3. Catherine Darnley (d.1743), daughter of Catherine Sedley and James II of England,  mar 1705. [Bio2]

His lovers were:

1. Barbara Villiers, 1st Duchess of Cleveland.

Lover in 1672

"Not content with Churchill as a lover, the following year Barbara took up with the Earl of Mulgrave (John Sheffield, a notorious roué, who later married James II's illegitimate daughter). Indeed it was reported by Lord Conway in November 1673 that Barbara was 'with child by Mulgrave and in no favor with the King.' Her situation was reminiscent of the Emperor Augustus's daughter Julia, who when she took a lover, would always liken herself to a merchant ship which only took on passengers when it had a full cargo! In this way Julia was able to preserve the legitimacy of her children. So for King Charles to acknowledge the child in the knowledge that her mother had had at least two lovers prior to her conception, was extraordinary indeed and only makes sense if he (Charles) was still having intermittent carnal relations with her." (Dewar & Powell. Royal Bastards)

2) Frances Stewart.

Natural offspring:

1. Charles (1646-1711)

Mary Kirke
Lady Vernon
@NPG

3) Mary Kirke, Lady Vernon (c1646-1711)

Maid-of-Honour to Mary, Duchess of York.

Also known as:

Mary Kirke, Lady Vernon

Mall Kirke.

Daughter of George Kirke, Groom of the Bedchamber to Charles II of England and Housekeeper of Whitehall Palace.

Sir Thomas Vernon
@NPG

Wife of Sir Thomas Vernon (1654-1721), 2nd Baronet of Hodnet, mar 1676, law reporter & politician.

"Mary Kirke was the daughter of George Kirke and his second wife, Mary Townshend and had been appointed maid-of-honour to the Duchess of York in 1674. After being mistress of Sir Thomas Vernon he married her after his first wife's death in 1676, but she ended her life in miserable circumstances at Greenwich in 1711. . . ." (Bulstrode. The Bulstrode Papers: Volume I (1667-1675): 304)

"George Kirke's second daughter, Mary ('Mall') Kirke, was a Maid of Honor to Marie Beatrice, Duchess of York, c1673-75. She seems to have been mistress (1) to the Duke of York, (2) to the Duke of Monmouth, and (3) to the Earl of Mulgrave. Apparently she tried to juggle all three at once. On October 1, 1674, a gossip reported that 'The Duke of Monmouth, being jealous of Lord Mulgrave's courting his newest mistress, Mall Kirke, watched his coming thence late four or five nights ago, and made the Guards keep him amongst them all night'. . . On June, 1675, we learn that Mall had long known that she was pregnant, had turned Roman Catholic, and had planned to retire to a nunnery on the continent for her confinement. But she waited too long 'and spoiled all.' Her infant was born tht morning with no midwife in attendance, just 'the young Mother of the Maids and her own servant.' The child died a few hours after birth. . . Mall was turned out of St. James's Palace and found refuge with her mother in Whitehall. On July 4 Percy Kirke challenged Lord Mulgrave 'for having debauched and abused his sister.' Mulgrave denied everything, and Mall denied any carnal relations with him, but the Restoration Hotspur would not be appeased; he fought with Mulgrave and wounded him seriously. On August 30 Mall fled to France and a nunnery 'to do penance for the rest of her life for her past follies'. (Wilson. Court Satires of the Restoration: 259)

"Charles Sackville's poem ;A faithful Catalogue of our most eminent Ninnies' ridiculed the conduct of 'that lustful tribe of Kirkes'; the younger daughter, Mary or 'Moll', was sarcastically singled out as the family's 'glory.' A maid of honour to the Duchess of York between December 1673 and 1675, she conducted near-simultaneous affairs with James Scott, 1st Duke of Monmouth and Buccleuch (1649-85), Charles II's oldest and favourite natural son; Charles's brother and heir, James, Duke of York; and John Sheffield, 3rd Earl of Mulgrave (1647-71), colonel of the Holland infantry regiment. Having contracted gravidity, possibly via Mulgrave, and Roman Catholicism, certainly from the Duke and Duchess of York, Mary resolved to withdraw unobtrusively to a French convent for her confinement but labour was premature and arrangements could not be made in time. Delivery occurred secretly in St James's Palace but the baby lived for only a few hours. . . ." (Childs. General Percy Kirke and the Later Stuart Army: 5)

" . . . Mary was later described as 'a beautiful wanton whose reputation did not improve with the years'. About this time she was having an affair with Lord Francis Villiers (1629-48), brother of George Villiers, 2nd Duke of Buckingham (1628-87). At the opening of the second Civil War in 1648, Villiers provided a splendid and lavish entertainment in Mary's honour and presented her with a gift of plate worth £1,000. When he was killed in action on 7 July 1648, a lock of her hair was discovered 'sew'd in a piece of ribbon that hung next to his skin'. . . ." (Childs. General Percy Kirke and the Later Stuart Army: 3)

"Monmouth also had an intrigue with Mary Kirke, a Maid of Honour to the Duchess of York (Mary of Modena) but appears to have shared her favours with the Duke of York and Lord Mulgrave. Warned of Mulgrave's interest in his mistress, Monmouth had him placed under house arrest in the palace guard house. Mulgrave retaliated by challenging one of the Duke's adherents, Mr. Felton, to a duel, Lord MIddleton and Mr. Buckley being seconds. Nine months later, in May/June 1675, the unfortunate maid 'had the ill fortune to become the mother of a boy, which however, died within 3 or 4 hours'. 'It was not said yet to which father it belongs'. 

" . . . The following year (1674) he was involved in a love triangle with Mary Kirke, a Maid of Honour to the Duchess of York, who was also sharing her favours with the Duke of Monmouth and the Duke of York. The child born of these proceedings, a boy, died a few hours after its birth. To his credit the lady never accused him 'of getting ye child or any other act' therefore the paternity must be laid at the door of one of the other participants." (Beauclerk-Dewar & Powell. Royal Bastards)

References.

Buckingham: The Life and Political Career of George Villiers, First Duke of Buckingham @Google Books
George Villiers, 2nd Duke of Buckingham, 1628-87 @British Civil Wars Project 
Men: George Villiers @Unusual Historicals.