Rumen Radev, backed by the socialist opposition is poised to become Bulgaria's President, exit poll results show.

Two pollsters are indicating Radev is leading by a wide margin in the runoff vote held on Sunday.

Sunday's result, if confirmed, would constitute the first ever election loss of Prime Minister Boyko Borisov since the party was set up in the mid-2000s.

They also mean his running mate, MEP Iliana Iotova, will be Vice President.

According to a 100% parallel count bu Alpha Research pollsters,, Radev has garnered some 59.7% of the vote.

Main ruling party's candidate Tsetska Tsacheva, nominated by Bulgarian Prime Minister Boyko Borisov, is trailing far behind at 35.6% of the vote.

Around 4.7% of voters have ticked the "I Do Not Support Anyone" option - or the so-called "protest vote" - that was introduced earlier this year.

Gallup International Balkan pollsters have projected nearly the same result, at 59.1%, 36.4%, and 4.5%, respectively.

Other polling agencies have yielded similar results which, however, are yet to be confirmed by electoral authorities.

Initial projections suggest Radev got the overwhelming support of all voters for candidates who polled worse in the first round, with the exception of Tsacheva's electorate (with more than 98% having backer her) and those who voted for right-wingers' candidate Traycho Traykov where more than 50% backed Tsacheva.

Turnout neared 48-50%. according to the pollsters.

Borisov earlier vowed to resign if Tsacheva lost the election.

He is yet to comment.

Labelled "pro-Russian" by his opponents and some Western and Russian media, Radev has been calling for a more pragmatic approach to foreign policy and steps to boost the judiciary, overhaul the armed forces and promote dialogue on how to raise the living standards.

You can read more about Radev here.