Brazilian President Jair Bolsonaro, who has been labelled “the Trump of the tropics,” has denied he harbours extreme fascist views and attempted to paint himself as a “Brazilian Churchill”.
Mrs May opted to break a long-standing political protocol by deciding not to call Mr Bolsonaro after he was elected - as is customary when world leaders come to power.
Number 10 announced the Prime Minister intended to send a letter, instead, as she gave the new Brazilian commander-in-chief the British cold shoulder.
But US President Donald Trump was not happy.
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The firebrand Republican was quick to rush to Mr Bolsonaro’s defence, tweeting: “We agreed that Brazil and the United States will work closely together on trade, military and everything else!”
Mr Bolsonaro replied: “We wish to bring these two great nations closer together and to advance on the path of freedom and prosperity.”
Trump revealed he’d exchanged “excellent” words with Mr Bolsonaro after he called to congratulate him earlier this week.
In the wake of his election, Mr Bolsonaro’s opponents clashed with law enforcement in Sao Paulo - a liberal, cosmopolitan centre.
A scourge of politically motivated violence also plagued Brazil throughout the campaign in defiance of Mr Bolsonaro’s extreme and controversial policies and opinions.
The Trump-like figure has vowed to make it easier to own firearms and has called for police to have more autonomy to shoot at criminals.
He is also staunchly against the legalisation of abortion and environmentalists fear his policies could wreak havoc on Brazil’s delicate and important eco-system.
In his victory speech, he said: "We cannot continue flirting with communism. We are going to change the destiny of Brazil.
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“The commitment I made to the Brazilian people was to create a decent government and I guarantee you that I will.”
Mr Bolsonaro experienced a sudden and rapid rise to power spearheaded by a rejection of the leftist Workers Party (PT).
PT ran Brazil for 13 of the last 15 years and presided over rampant corruption and successive impeachments.
But the party was ousted two years ago as a political scandal and a deep recession gripped the South American nation.
Strident lawmaker Mr Bolsonaro surged in popularity amid the Brazilian people’s increasing disillusionment with corruption in politics.
Mr Bolsonaro, who compared his campaign to Trump's 2016 run, has dismissed as “fake news” accusations of sexism, racism and homophobia levelled against him.
The hard-line politician, who has campaigned on an anti-socialist stance, vows an unforgiving crackdown on crime and political corruption as he attempts to win over the disenfranchised Brazilian electorate.