EU member Bulgaria faced an uncertain future on Monday after centre-right Prime Minister Boyko Borisov quit following the crushing defeat of his presidential nominee at the hands of a Moscow-friendly general backed by the Socialist opposition.
Critics fear the surprise win could tilt ex-communist Bulgaria, which has long walked a tightrope between Moscow and Brussels, towards Russia's orbit -- a trend seen across eastern and central Europe amid rising euroscepticism.
Nearby Moldova also looked set to elect a pro-Russian president on Sunday.
"The results clearly show that the ruling coalition no longer holds the majority," the premier, who was re-elected in 2014 for a second time, said on Sunday evening.
"I apologise to those who supported us. I thought I was doing the right thing."
The announcement came shortly after projections showed that ex-airforce chief and political novice Rumen Radev had swept close to 60 percent of ballots. Borisov's nominee ex-parliament speaker Tsetska Tsacheva obtained just over 35 percent, in what political analysts calls a "catastrophic defeat".
The straight-laced Tsacheva meanwhile failed to sway voters disgruntled over the government's perceived failure to tackle rampant corruption and poverty in the European Union's poorest member state.
Gallup director Parvan Simeonov told AFP the outcome was a "clear protest vote".
Despite promised reforms, graft and poverty remain rife in the EU's poorest member state, while public anger has also grown over thousands of migrants currently stranded in Bulgaria.
"Bulgaria needs a new face, someone who defends national interests instead of always saying 'Yes' to the European Union and the United States," businessman and Sofia resident Assen Dragov, 39, told AFP Sunday.
The Bulgarian president's role is largely ceremonial but the incumbent is nonetheless a respected figure and commander-in-chief of the armed forces.
'Seek dialogue' with Russia
Radev is due to take office on January 22 for a five-year term. His first job will likely be to call early elections in spring next year, after Borisov said Sunday he would refuse to form an interim government.
Although GERB remains the country's top political force, opinion polls indicate it will not be able to obtain an outright majority.
National security and preventing a new migrant influx were key points of Radev's campaign, which saw the general gaining confidence and projecting himself as a fierce critic of the conservative status-quo.
His 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 could pursue closer ties with Moscow.
"General Radev's victory represents the unfolding of a pro-Russian scenario in Bulgaria so that the country supports Russian interests in the EU and NATO," political expert Antoniy Galabov told AFP.
In his victory speech, Radev reiterated his support for scrapping the sanctions and also praised new US president-elect Donald Trump for "seeking more dialogue" with President Vladimir Putin.
"This gives a lot of hope for reducing (the risk) of confrontation, particularly in Syria" where Russia and the US are backing opposite sides in a bloody civil war, Radev said.
His victory signals a change of direction from outgoing President Rosen Plevneliev, a strong critic of Moscow.
Plevneliev warned Sunday that Russia was trying to "destabilise Europe" by financing anti-EU ultra-nationalists in Balkan states including in Bulgaria.