Alongside Mihhail Kõlvart, Yana Toom and Vadim Belobrovtsev, Mr Kaljulaid was one of four Centre Party board members who had voted against launching coalition talks with EKRE.

Centre's Monday decision shocked Estonian society, he said, but its Russian community in particular, whose interests the party has represented.

"EKRE politicians have repeatedly minimised Hitler's crimes," Mr Kaljulaid wrote in his blog. "One of its politicians has referred to childless women as a 'harmful element to society,' and another, as MP, has told allied troops to wear their uniforms if they don't want to get beaten up! During the course of its election campaign, EKRE has employed tricks that may not be used. Their results have been achieved dishonestly and with deceit. Their economic programme is absurd and its implementation would in no way improve the welfare or wages of the people of Estonia. This bunch lacks a sense of responsibility before the state. What government are we talking about with them?"

As a result, Mr Kaljulaid found that the Centre Party board's decision left him with two options — to either accept it, or to resign from the board. "I cannot accept this decision, and so I am resigning from the board," he wrote.

Nonetheless, he hopes that his decision will make the rest of the board reconsider and reevaluate all circumstances.

"If Centre wants to command any sort of respect in Estonian society in the future, it has to abandon this awful coalition before it can be formed," he added.

Better splinter than help EKRE to power

In an interview with ERR on Tuesday, Mr Kaljulaid said that he hopes to convince the Centre Party council not to confirm any possible coalition agreement with EKRE, but considers it possible that the party may split over this issue.

"The risk that the Centre Party will splinter definitely exists, but I find that if on one hand you have the extreme right-wing and populistic EKRE reaching Estonia's executive [branch], then honestly, if it's necessary to risk the Centre Party splintering in order to avoid it, then better the Centre Party splinter, just don't let this government happen," he said.

Commenting on the effect the possibility of the Centre Party forming a government with EKRE might have on Centre voters, Mr Kaljulaid said that this will deter more than just the party's Russian-language supporters.

"It seems to me as though many observers and analysts have made a great mistake here if they think that this is only a problem for Russian-speaking voters," he said. "My initial impression of the first 24 hours since the public became aware of this plan is that both Centre Party voters representing the Russian-language community as well as very, very many other people who supported the Centre Party's candidates in the latest elections, including me, and who are Estonians or of other ethnic backgrounds altogether are equally against it."

The current city district elder of Põhja-Tallinn also believed it unlikely that Estonia's Jewish community would be pleased over a party whose politicians have downplayed the crimes against humanity committed by Hitler's regime ending up in the government.

"And I think that the young generation of Estonians in particular feels like Brits did the morning after the Brexit vote or young Americans felt when they saw that Donald Trump had won the [US] presidential elections," he added.

Nonetheless, Mr Kaljulaid expressed hope that the party will ultimately decide against supporting the formation of a coalition with EKRE.

"Right now, I see the Centre Party coming to its senses as a solution," he said. "This means that either the board of the Centre Party or the Centre Party parliamentary group rejects this proposal. I hope to send a message to my colleagues — now former colleagues, on the board — with my resignation as well that this is a matter that needs to be considered again and very carefully, and that [the Centre Party] has to reconsider what this will cost Estonia, Estonian society, the cohesion of Estonian society, and then consider whether it is still worth going this route."

Toom: Board now 14:3

Centre board member Yana Toom on Tuesday expressed support for Mr Kaljulaid, but also indicated that it wasn't necessary to quit the board in order to reverse the party's course.

"I fully share Raimond Kaljulaid's position on EKRE and understand his feelings very well," Ms Toom wrote on social media late Tuesday morning. "But unless and until a coalition agreement has been signed, I don't believe that all options have been exhausted. One doesn't have to shrug off responsibility in order to change something."

She noted that with Mr Kaljulaid's departure, the party board is now 14:3 in favour of launching coalition talks with EKRE and Isamaa.

Any coalition agreement involving the Centre Party must also be confirmed by the party council.