Helena Kantakouzene
Helena Kantakouzene (1333 – 10 December 1396) was the Empress consort of John V Palaiologos in the Byzantine Empire.
Peter Burroughs
Peter Burroughs( born 27 January 1947) is a British television and film actor, the director of Willow Management.
He is the father- in- law of actor and TV presenter Warwick Davis.
Irene of Trebizond
Irene of Trebizond( died around 1382) was the bigamous wife of Basil of Trebizond, by whom he had two sons, Alexios and John( later Alexios III of Trebizond), and possibly three daughters Anna, Maria and Theodora.
Rusudan of Georgia, Empress of Trebizond
Rusudan of Georgia, Empress of Trebizond was a consort of Manuel I of Trebizond, and the mother of Empress Theodora.
Very little is known for certain about her.
Ogawa Mataji
Viscount was a general in the early Imperial Japanese Army.
He was also the father- in- law of Field Marshal Gen Sugiyama.
David of Trebizond
David Megas Komnenos (– 1 November 1463) was the last Emperor of Trebizond from 1459 to 1461.
He was the third son of Emperor Alexios IV of Trebizond and Theodora Kantakouzene.
Following the fall of Trebizond to the Ottoman Empire, he was taken captive with his family to the Ottoman capital, Constantinople, where he and his sons and nephew were executed in 1463.
In July 2013, David and his sons and nephew were canonized by the Holy Synod of the Patriarchate of Constantinople.
Their feast day was determined as 1 November, the anniversary of their deaths.
Irene Palaiologina of Trebizond
Irene Palaiologina
( Greek: Ειρήνη Παλαιολογίνα," Eirēnē Palaiologina"),( c. 1315 – after 1341) was Empress of Trebizond from April 6, 1340 to July 17, 1341.
She was an illegitimate daughter of the Byzantine Emperor Andronikos III Palaiologos, and she married Emperor Basil of Trebizond in 1335.
Maria of Gothia
Maria of Gothia was the first wife of David of Trebizond, last Emperor of Trebizond, whom she married in 1426.
Anna of Trebizond
Anna Anachoutlou( died 1342) was Empress of Trebizond from July 17, 1341, to September 4, 1342.
Anna was the elder daughter of Emperor Alexios II of Trebizond and his Georgian wife, Djiadjak Jaqeli.
Helena Kantakouzene, Empress of Trebizond
Helena Kantakouzene (died 1463) was the second wife of David of Trebizond, the last Emperor of Trebizond.
Recent research has led to doubts regarding her existence.

Question: Who is the father-in-law of Helena Kantakouzene, Empress Of Trebizond?
Answer: Alexios IV of Trebizond