© AFPRumen Radev, candidate of the opposition Socialists, attends a news conference, in Sofia on November 6.
The center-right prime minister told reporters after the vote on November 13 that he would formally hand in his resignation on November 14 or 15, because "the results clearly show that the ruling coalition no longer holds the majority."
Borisov's resignation is likely to trigger early elections in the spring of 2017 and risks plunging the NATO-member and EU-member country into renewed political turmoil just two years after Borisov took office for his second term.
Projections show that former Bulgarian Air Force chief and political novice Rumen Radev won nearly 60 percent of the vote on November 13.
His rival, former parliament speaker Tsetska Tsacheva, obtained just over 35 percent.
Observers say the surprise win could tilt Bulgaria back toward Russia's orbit -- a trend seen increasingly in Eastern and Central Europe amid rising skepticism about the EU.
The Bulgarian presidency is a largely ceremonial position, but the president can influence government policy.
What I think we are seeing happening in the West, and NATO states is a result of there complete lack of understanding of the needs of the people who elected hem.
There concerns about the loss of employment, resulting in financial insecurity, employment insecurity, the fear of being unable to take care of there families, the fear that they will not be able to give there children a future. And also the infrastructure where they live, cities and towns. Is it working for them, after all that is where part of there taxes go.
And indeed I think that is the concern of many, many people in the world, regardless of where they live.