Kyril was born in Madrid, and graduated from Princeton University in 1986, having completed a bachelor degree in Physics.
In 2007 he worked for GLG Partners, the London-based asset management branch of Lehman Brothers.
Kyril married Doña María del Rosario Nadal y Fuster de Puigdórfila on 15 September 1989. Nadal is a maternal descendent of the Counts of Olocau, her grandfather being the 9th Count, and her uncle being the present and 10th Count. Rosario is also a descendant of the Aztec Emperor Moctezuma II.
The religious ceremony was held at Saint Anne's Chapel, Almudaina Palace, Palma de Mallorca. The Spanish tabloids ¡Hola! and Semana covered the event and reported that there were 400 guests, though only 125 could be accommodated in the chapel for the religious ceremony. According to Majesty magazine at the time, King Juan Carlos, Queen Sofía, Infanta Elena, Infanta Cristina, and Felipe, Prince of Asturias, attended the occasion.
The couple have three children: Mafalda-Cecilia (born 27 July 1994), Olimpia (born 14 December 1995), and Tassilo (born 20 January 2002).
A former model and muse for the fashion designer Valentino, Rosario is, by profession, a consultant and professor of art history. In 2007, she wrote an article for Architectural Digest.
In October 2009, it was announced by the Spanish news agency EFE that, according to a report from an anonymous source close to Simeon of Bulgaria, the couple were going to live separately. The source claimed, however, that they don't presently have any plans or intention to divorce.
The couple appeared together at the wedding of Princess Victoria of Sweden in June 2010.
On 28 October 1987, Kyril escorted fellow Princeton graduate Brooke Shields to a dinner/fashion show hosted by Christian Lacroix in New York City. Until his marriage, Kyril's purported romantic interests were tracked by European celebrity magazines, notably ¡Hola! in Spain.
He owns a vacation residence near Campos, Majorca, where he is a keen surfer.
He and his wife have been known to socialize with many celebrities and royalty, such as Gwyneth Paltrow, Hugh Grant, the Crown Prince Haakon Magnus and Mette Marit of Norway, as well as the Spanish royal family.
He is the godfather of Prince Aristidis-Stavros of Greece and Denmark, son of Pavlos, Crown Prince of Greece.11 July 1964 – present: His Royal Highness Prince Kyril of Bulgaria, The Prince of Preslav, Prince of Saxe-Coburg and Gotha, Duke of Saxony
Bulgarian royal family: Knight Grand Cross of the Order of St Alexander