After the fall of Constantinople in 1453, certain members of the vast Kantakouzenos family reached the Romanian principalities (Wallachia and Moldavia), where they managed to grow influential and powerful once more.

Staying in the vicinity of the Carinthian Gate, in a heavily populated suburb, Păuna hoped to get recognition and support from the Habsburgs to install Radu as Prince of Wallachia.

[5] Faced with the unlikelihood of her son's accession, Păuna first hoped to send Radu to live out his life in exile the Netherlands, but was unable to do so.

[9] After negotiating with Eugene of Savoy, Păuna instead managed to secure Radu's entry into the imperial army in the spring of 1718,[5][9] as well as a pension of 2,000 florins.

[1][9] At an unspecified date, Păuna, Radu and Constantin travelled to Russia, where Emperor Peter the Great placed them under the protection of Dimitrie Cantemir.

Radu also travelled to Warsaw, meeting with the Polish king Augustus the Strong, and to Venice, seeking to offer his services in exchange for funds.

[10] Radu returned to Vienna, where he grew increasingly dissatisfied with the family's poor residence and their scant imperial support, which clashed with his and Constantin's self-image.

In the letter, the two brothers complained that they were unable to maintain the dignity of their rank due to their lack of funds, and that they did not even have a single carriage, even though they were "not accustomed to walking".

Radu and Constantin had sought to extend their pension to 5,000 florins, but Emperor Charles VI instead retracted the individual bonuses that had previously been granted to the brothers.

[6] Faced with economical problems and a perceived loss of dignity, Radu turned to an unorthodox method of raising his income: exploiting and exaggerating the illustrious origins of his family.

[16] In addition to bestowing the grand mastership upon him, the 1735 document also formally recognized Radu as a prince, and as a "descendant of the Roman emperors of the East and West".

[23] The Habsburg government accepted Radu's request due to fear that he might otherwise offer his services elsewhere, given that the Cantacuzino name was influential in the Balkans and that his departure from the empire could cause "unwanted mischief".

[25] The banners of Radu's regiment displayed religious figures, such as John the Baptist and Saint Nicholas, as well as animals, such as lions or eagles.

[23] In addition to the other factors, Radu was also viewed as an inappropriate grand master given that he had given out knighthoods not only to nobles, but also to commoners and rich merchants in exchange for money.

[25] His reputation destroyed and being faced with considerable debt, Radu fled Vienna early in 1745,[23] narrowly escaping being put on trial for high treason.

[28] In 1746, Radu's brother Constantin and his followers, including the nobleman Vlad Boțulescu, were arrested on charges of conspiracy against the state and were sentenced to life in prison.

[27][25] After leaving Vienna, Radu first travelled to Prussia, offering his services to Frederick the Great, but he was refused on the basis of his past history.

Radu even went as far as begging to Frederick's mother, Sophia Dorothea of Hanover, to be allowed to stay, and tried to convince the Prussians to let him serve them on the basis of his ability to gather Romanians and other Balkan exiles under his leadership.

Radu and his wife Elisabeth spent the rest of their lives wandering around Europe in poverty, avoiding hostile imperial authorities.

[22] Radu was survived by five children: the four daughters Leopoldina, Cecilia, Maria and Elisabeta, all married to noblemen, and the son George, born in 1738 and dead in 1771, who served in the Habsburg military.

Nicolae Iorga wrote in 1933 that Radu was a "restless and vicious man, eager for all begging and all betrayals, greedy for honors and especially money, who so cruelly compromised the fame of a family with such brilliant origins and such a purpose".