Question: Who is Catherine I, Latin Empress's father-in-law?

Knowledge 1: Catherine I, Latin Empress
Catherine I, also Catherine of Courtenay (25 November 1274 – 11 October 1307), was the recognised Latin Empress of Constantinople from 1283 to 1307, although she lived in exile and only held authority over Crusader States in Greece.In 1301, she became the second wife of Charles of Valois, by whom she had one son and three daughters; the eldest of these, Catherine II of Valois, Princess of Achaea succeeded her as titular empress. [SEP] Knowledge 2: Charles, Count of Valois
Charles of Valois (12 March 1270 – 16 December 1325), the third son of Philip III of France and Isabella of Aragon, was a member of the House of Capet and founder of the House of Valois, whose rule over France would start in 1328.Charles ruled several principalities.He held in appanage the counties of Valois, Alençon and Perche.Through his marriage to Margaret of Anjou, he became Count of Anjou and Maine.Through his marriage to Catherine I, titular empress of the Latin Empire, he was titular Latin Emperor of Constantinople from 1301–1307, although he ruled from exile and only had authority over Crusader States in Greece.The grandson of Louis IX of France, Charles of Valois was a son, brother, brother-in-law and son-in-law of kings or queens (of France, Navarre, England and Naples).His descendants, the House of Valois, would become the royal house of France three years after his death, beginning with his son Philip VI of France.
Knowledge 1: Charles, Count of Valois
Charles of Valois (12 March 1270 – 16 December 1325), the third son of Philip III of France and Isabella of Aragon, was a member of the House of Capet and founder of the House of Valois, whose rule over France would start in 1328.Charles ruled several principalities.He held in appanage the counties of Valois, Alençon and Perche.Through his marriage to Margaret of Anjou, he became Count of Anjou and Maine.Through his marriage to Catherine I, titular empress of the Latin Empire, he was titular Latin Emperor of Constantinople from 1301–1307, although he ruled from exile and only had authority over Crusader States in Greece.The grandson of Louis IX of France, Charles of Valois was a son, brother, brother-in-law and son-in-law of kings or queens (of France, Navarre, England and Naples).His descendants, the House of Valois, would become the royal house of France three years after his death, beginning with his son Philip VI of France. [SEP] Knowledge 2: Beatrice of Sicily, Latin Empress
Beatrice of Sicily (1252 – 17 November/12 December 1275) was titular Latin Empress as the wife of Philip of Courtenay.Her parents were Charles I of Sicily and Beatrice of Provence.Under the Treaty of Viterbo (27 May 1267), Baldwin II of Courtenay transferred much of the rights to the Latin Empire to Charles I. Charles was to be confirmed in possession of Corfu and some cities in Albania.He was also given suzerainty over the Principality of Achaea and sovereignty of the Aegean Islands, excepting those held by Venice and Lesbos, Chios, Samos, and Amorgos.The same treaty arranged the marriage of Philip of Courtenay, heir apparent to the Latin Empire, and Beatrice, second daughter of Charles.If the marriage was childless, Philip's rights would be inherited by Charles I. Beatrice was approximately fifteen-years-old at the time of her betrothal.On 15 October 1273, Beatrice and Philip were married in Foggia.The bride was twenty-one-years old and the groom thirty.Her father-in-law died days later.Philip was proclaimed emperor with Beatrice as empress.The marriage was harmonious and produced a daughter, Catherine I of Courtenay, born on 25 November 1274.Beatrice died in late 1275 after a short illness.
Knowledge 1: Catherine I, Latin Empress
Catherine I, also Catherine of Courtenay (25 November 1274 – 11 October 1307), was the recognised Latin Empress of Constantinople from 1283 to 1307, although she lived in exile and only held authority over Crusader States in Greece.In 1301, she became the second wife of Charles of Valois, by whom she had one son and three daughters; the eldest of these, Catherine II of Valois, Princess of Achaea succeeded her as titular empress. [SEP] Knowledge 2: Beatrice of Sicily, Latin Empress
Beatrice of Sicily (1252 – 17 November/12 December 1275) was titular Latin Empress as the wife of Philip of Courtenay.Her parents were Charles I of Sicily and Beatrice of Provence.Under the Treaty of Viterbo (27 May 1267), Baldwin II of Courtenay transferred much of the rights to the Latin Empire to Charles I. Charles was to be confirmed in possession of Corfu and some cities in Albania.He was also given suzerainty over the Principality of Achaea and sovereignty of the Aegean Islands, excepting those held by Venice and Lesbos, Chios, Samos, and Amorgos.The same treaty arranged the marriage of Philip of Courtenay, heir apparent to the Latin Empire, and Beatrice, second daughter of Charles.If the marriage was childless, Philip's rights would be inherited by Charles I. Beatrice was approximately fifteen-years-old at the time of her betrothal.On 15 October 1273, Beatrice and Philip were married in Foggia.The bride was twenty-one-years old and the groom thirty.Her father-in-law died days later.Philip was proclaimed emperor with Beatrice as empress.The marriage was harmonious and produced a daughter, Catherine I of Courtenay, born on 25 November 1274.Beatrice died in late 1275 after a short illness.

Answer: Philip III of France