Members of the family claim that the genealogical links between the Byzantine Greek and Romanian branches of the family have been extensively researched. The family first appears among the Phanariotes in the late 16th century, with Michael "Şeytanoğlu" Kantakouzenos, after a gap of over a century from the Fall of Constantinople. Whether the family is indeed linked to the Byzantine imperial house of Kantakouzenos is disputed, as it was usual among wealthy Greeks of the time to assume Byzantine surnames and claim descent from the famous noble houses of their Byzantine past. The eminent Byzantinist Steven Runciman considered the latter-day Kantakouzenoi "perhaps the only family whose claim to be in the direct line from Byzantine Emperors, as authentic", but according to the historian Donald Nicol, "Patriotic Rumanian historians have indeed labored to show that... of all the Byzantine imperial families that of the Kantakouzenos is the only one which can truthfully be said to have survived to this day; but the line of succession after the middle of the fifteenth century is, to say the least, uncertain." The origin of the Byzantine family can be traced to Smyrna. The Greek scholar Konstantinos Amantos suggested that "Kantakouzenos" derives from κατὰ-κουζηνᾶν or κατὰ-κουζηνόν, ultimately from the locality of Kouzenas, a name for the southern part of Mount Sipylon near Smyrna. Donald Nicol agrees with this theory, and lists some connections the Kantakouzenoi had with the locale in the 11th and 13th centuries.
Origin of the Romanian branch
The Greek Kantakouzenos family had been active in Constantinople and Greece during the Greek War of Independence, but several branches of the original Greek family were created via the migrations and establishment of Kantakouzenos family members to different parts of Europe. Two of those new branches were the Romanian Cantacuzino branch as well as the Russian branch. As a consequence of the Russian Revolution and the Soviet occupation of Romania after World War II, the last two branches now mostly live in Western Europe and North America. According to Jean-Michel Cantacuzène and Mihail Sturdza, the origin of the Cantacuzino family in Romania is traced to Andronikos Kantakouzenos, a Greek financier from Constantinople, son of the "Prince of the Greeks" Michael "Şeytanoğlu" Kantakouzenos. Andronikos had among his several sons two who became "boyars" in what today is Romania and founded the yet-surviving new branches of Cantacuzino:
"boyar" Georgios 'Iordaki' Kantakouzenos became forefather of the Moldavian branch, which soon branched to Cantacuzino-Deleanu and Cantacuzino-Pasceanu.
"boyar" Konstantinos 'Kostaki' Kantakouzenos married an heiress of the late reigning princeRadu Șerban, onetime ruler of Wallachia, and they founded the Wallachian branches which soon clashed against the Ghica family over power.
