"The King [sein Vater Ludwig XIV.] loved him tenderly, and everybody at Court shared this predilection of the Monarch. M. de Vermandois, of a stature less than his father, was none the less one of the handsomest cavaliers at the Court. To all the graces of his amiable mother he joined an ease of manner, a mixture of nobility and modesty, which made him noticeable in the midst of the most handsome and well-made. I [Madame de Montespan] loved him with a mother's fondness, and, from all his ingenuous and gallant caresses, it was easy to see that he made me a sincere return. This poor Comte de Vermandois, about a year before the death of the Queen [also um 1682], had a great and famous dispute with Monsieur le Dauphin, a jealous Prince, which brought him his first troubles, and deprived him suddenly of the protecting favour of the Infanta-Queen. ... Some time after that, Messieurs de Conti, great lovers of festivity, pleasure and costly delights ... dragged the Comte de Vermandois ... into one of those licentious parties where a young man is compelled to see things which excite horror. His first scruples overcome, M. de Vermandois, naturally disposed to what is out of the common, wished to give guarantees of his loyalty and courage; from a simple spectator he became, it is said, an accomplice. There is always some false friend in these forbidden assemblies. The King heard the details of an orgy so unpardonable, and the precocious misconduct of his cherished son gave him so much pain, that I saw his tears fall. The assistant-governor of the young criminal was dismissed; his valet de chambre was sent to prison; only three of his servants were retained, and he himself subjected to a state of penitence which included general confessions and the most severe discipline. He resigned himself sincerely to all these heavy punishments. He promised to associate only with his mother, his new governor, his English horses and his books; and this manner of life, carried out with a grandeur of soul, made of him in a few months a perfect gentleman, in the honourable and assured position to which his great heart destined him. The King, satisfied with this trial, allowed him to go and prove his valour at the sieges of Dixmude and Ciurtrai. ... A few days afterwards we learned at Versailles that M. de Vermandois was dead, in consequence of an indisposition caught whilst bivouacking, which at first had not seemed dangerous. ... M. le Comte de Vermandois left by his death the post of High-Admiral vacant. The King begged me [Madame de Montspan] to bring my little Comte de Toulouse [das jüngste Kind von Madame de Montespan und dem König]; and passing round his neck a fine chain of coral mixed with pearls, to which a diamond anchor was attached, he invested him with the dignity of High-Admiral of France." (in: Memoirs of Madame la Marquise de Montespan, Volume 2, pp. 311-312/316-318/321-322).
Zum Leidwesen seines Vaters, des französischen Königs Ludwig XIV., stellte sich heraus, dass Louis wie sein Onkel Philippe I., der Herzog von Orléans, am "italienischen Laster", der Homosexualität, litt. Auch eine im Frühjahr 1682 aufsehenerregende Säuberungsaktion sollte dieses "Laster" nicht beseitigen. Von seinen Zeitgenossen wurde Louis als "schön - obwohl er ein wenig schielte -, jung und gut gebaut" beschrieben. Sophie von Pfalz, die Kurfürstin von Hannover, die ihm 1679 begegnet war, beschrieb ihn als "sehr liebenswert".