Rumen Radev, Bulgarias surprise new Russophile president-elect, is a former flying ace with no political background who critics say could try to steer the EUs poorest country back into Moscows orbit.

The MiG pilot and former Bulgarian air force chief of staff, more used to a uniform than a suit, won close to 60 percent of ballots in a closely-fought run-off on Sunday, projections showed.

The 53-year-old, little known previously, beat the personal nominee of centre-right Prime Minister Boyko Borisov, ex-parliament speaker Tsetska Tsacheva, who fell short with just over 35 percent.

Radev graduated from Bulgaria's Air Force University and Rakovski Defence and Staff College and specialised in the US Air War College in Maxwell Air Force Base.

He started his military career as junior pilot in 1987-88 and moved up the ranks to become Bulgaria Air Force deputy commander from 2009 to 2014, when he stepped up in the commander's seat.

Bumpy ride with Borisov

Radev has taken Borisov to task over his failure to improve the lot of the many Bulgarians living in dire poverty and the lack of progress in stamping out rampant corruption.

He had already crossed swords with Borisov in his air force days, when he pressed hard for the acquisition of new rather than used fighter jets, finally leaving office earlier this year in a huff.

He was then invited by the main opposition Bulgarian Socialist Party as their candidate for president.

His election campaign stressed national security and preventing a new migrant influx, and he gained confidence projecting himself as a fierce critic of the conservative status quo.

"He will unify the nation... and he knows how to defend his positions," his father, Georgi Radev, said on Sunday evening in the southeastern village of Slavianovo, which celebrated the news.

His first job as new president -- a largely ceremonial role -- will be to call early elections in March, after Borisov announced he would resign shortly after news broke of Tsacheva's crushing defeat.

Closer ties with Russia

Radev's clear support for the lifting of EU sanctions on Russia over Ukraine and ambivalent statements about the EU and NATO have prompted analysts to speculate that he might pursue closer ties with Moscow.

"I am convinced that the sanctions do not help but only harm... Russia and the EU countries are equally hurt," Radev said during the campaign.

Bulgaria's membership into the EU and NATO "has no alternative but it does not necessarily mean that we must declare ourselves enemies of Russia", he added.

He also shocked observers by repeatedly saying that Crimea "is de jure Ukrainian but de facto Russian".

Radev is married and a father of teenage daughter and son from a previous marriage. He speaks English, German and Russian.

He will be sworn in on January 22 for a five-year term in office.