Helena Kantakouzene (; 1333 – 10 December 1396) was the Empress consort of John V Palaiologos in the Byzantine Empire. Life She was a daughter of John VI Kantakouzenos and Irene Asanina; Donald Nicol believes she was the youngest of their three daughters. She was a sister of Matthew Kantakouzenos and Manuel Kantakouzenos. Her sisters Maria and Theodora were the respective wives of Nikephoros II Orsini and Orhan I. John V and John VI were rival emperors in a civil war fought from 1341 to 1347. The two sides at last reached an agreement. According to its terms John VI would be recognized as senior co-emperor with John V as his junior. The peace was sealed with the marriage of Helena to John V. The marriage occurred on 28 May 1347 – 29 May 1347, on the eighth day after her father's coronation by the Patriarch Isidore. Helena was about thirteen years old while her groom was a month short of his fifteenth birthday. Peace only lasted until 1352 when her husband resumed hostilities against her father. John VI was forced to resign the throne on 4 December 1354. Her brother Matthew would retain his title as co-emperor until his own defeat in 1357. Previous to her marriage, Helena had accompanied her mother and sister to Selymbria for the wedding of her sister Theodora to the Ottoman Emir Orhan in 1346. Shortly after her own wedding, Orhan sent an agent to Constantinople to assassinate her husband, thinking he was doing John VI Kantakouzenos a favor. In 1352 Helena accompanied with her husband and her younger son Manuel to Thrace to accept control of the cities John VI had allotted him. Nicephorus Gregoras claims she later went to Constantinople to protect her father from possible actions by her husband, who had joined the anti-Palamite cause. When her son Andronikos IV deposed his father 12 August 1376 in the struggle of the ongoing civil war, Helena tried to reconcile the two parties. Despite her efforts, John V and his sons Theodore and Manuel were put in prison October of that year. When the three escaped from prison in June 1379, she was thought responsible for it. Andronikos IV then fled to Galata, taking with him as hostages Helena, her elderly father John VI, and her two sisters Maria and Theodora. There the four were kept in strict confinement and suffered increasing privation