Monsieur's favourite and sexuality
There is some debate as to when Lorraine became the lover of the duke of Orléans (known as Monsieur at court), with hypotheses ranging from 1658 to 1668. Based on the account of Daniel de Cosnac, Monsieur's confessor, Pieragnoli argues that the affair likely began sometime in the winter of 1666-1667. Barker generally concurs, placing the beginning of Monsieur's and Lorraine's relationship during the 1667-1668 War of Devolution.
During the War of Devolution, the duke requested that the chevalier and his Harcourt Regiment be placed under his command; after initially denying his brother's request, the king eventually approved it. On the night of 24-25 August 1667, Lorraine was wounded in the foot by a grenade during an assault at Lille; contemporaries noted that Monsieur had him moved to his own tent and that Monsieur passed entire days there. Following his return from the campaign in Flanders, Monsieur declared "that he had resolved to distinguish [Lorraine] from all others in the realm [and] to give him a place in his house." Upon arriving at the Château de Villers-Cotterêts, Cosnac records that Lorraine "was received by Monsieur with incredible joy. From that moment, [Monsieur's] favour had been declared." Monsieur and Lorraine were for days inseparable.
Lorraine remained Monsieur's maître en titre (official favourite) or favori déclaré (declared favourite) from the end of the 1660s to the end of the duke's life in 1701, in a "long-term partnership in a very modern sense." As such, Lorraine was entrusted with running the Orléans household. In this capacity he oversaw the duke's finances; ran the duke's residences at the Palais-Royal and the Château de Saint-Cloud; and exercised some influence over household appointments and dismissals. At times during their relationship, Lorraine and the duke lived in a ménage à trois with Antoine Coëffier de Ruzé, Marquis d'Effiat or Charles, Count of Beuvron.
Primi Visconti relates that beginning in the 1670s, Lorraine supplied young men to Monsieur's court, without removing himself as an option as a partner. He kept himself in favour by controlling who Monsieur would have affairs with, without putting himself "outside the ranks."
By the end of the 1670s, Monsieur seems to have considered Lorraine a spouse: on the occasion of her visit, Monsieur insisted that Sophie of Hanover kiss Lorraine, as she was expected to do only with members of the royal family.
The relationship between the Lorraine and the duke reportedly affected Monsieur's first marriage to Henriette Stuart. Saint-Simon indicates that the duke of Orléans declared he could not love his wife without Lorraine's approval, contributing to marital tensions.
Contemporary correspondence and later memoirists attest to the tension between Lorraine and Henriette, as well as to Philippe's limited discretion regarding his long-standing relationship with Lorraine.
According to Henriette, Elizabeth Charlotte, and Saint-Simon, Lorraine frequently manipulated the duke of Orléans. The duke of Orléans married Elizabeth Charlotte of the Palatinate in 1671, who later wrote of Lorraine:
Philippe de Lorraine was three years younger than Philippe d'Orléans. Insinuating, brutal and devoid of scruple, he was the great love of Monsieur's life. He was also the worst enemy of the latter's two wives. As greedy as a vulture, this younger son of the French branch of the House of Lorraine had, by the end of the 1650s, hooked Monsieur like a harpooned whale. The young prince loved him with a passion that worried Madame Henriette and the court bishop, Cosnac, but it was plain to the King that, thanks to the attractive face and sharp mind of the good-looking chevalier, he would have his way with his brother.
Lorraine's relationship with the second Madame was complex; although she did not fault Monsieur or his favourites for their homosexual relationships, she complained of Monsieur's tendency to overspend on his favourites and of Lorraine's having "poisoning [Monsieur's] soul" against her. They had reconciled by the end of the 1690s.
Lorraine was likely bisexual, having had recorded relationships with several people of both genders (many of which occurred during his relationship with Monsieur), including Elizabeth de Fiennes, Louise-Elizabeth de Rouxel, Madame de Grancey (it was rumoured that Lorraine had sons with both Fiennes and Grancey), Monsieur, Effiat, and possibly Armand de Gramont, Comte de Guiche.