Prime Minister David Cameron has written to Taoiseach Enda Kenny on the eve of the Irish election wishing him well.
In an unusual move just hours before the opening of polling stations, Mr Cameron sent a letter to Mr Kenny saying he was "profoundly grateful" for his support on the recent Brexit negotiations.
And he put a personal note at the end, reading "My very best wishes for tomorrow's election" before adding "Good luck!"
The timing is seen as unusual given Prime Ministers tend to steer clear of anything that could be construed as an endorsement of another politician during the course of an election campaign.
However, Mr Cameron credited the Fine Gael leader with "helping" him secure a successful outcome at last week's European Council meeting.
"It made a real difference, and I am profoundly grateful to you," he wrote.
Sources in the Government have said that Mr Cameron considers the Taoiseach one of his closest allies in Europe and would like to see him re-elected - although he could never state this outright.
"They have worked well together and it would be a case of starting from scratch if somebody else is elected," said the source.
In his letter, dated February 26 and signed "David", the Conservative leader said that he was "especially grateful for the patience and understanding" Mr Kenny showed during the talks and for his "readiness to be creative in exploring all possible solutions".
The Taoiseach has made several public speeches backing a vote for the UK to stay within the European Union.
Last month Mr Cameron was perceived to have come close to publicly endorsing Mr Kenny during a joint Press conference when he said he looked forward to working with the Taoiseach "in the months and years ahead".
But yesterday's letter will be seen in political circles as even more significant.
There was controversy during the 2007 election when then Prime Minister Tony Blair invited Bertie Ahern to address Westminster mid-campaign.
The historic speech gave Mr Ahern an opportunity to focus attention on his work for the peace process at what was a very difficult time for his personal popularity.
Meanwhile, Mr Kenny and Tanaiste Joan Burton staged a Press conference yesterday to appeal to voters to re-elect the Fine Gael-Labour coalition.
Mr Kenny said he had worked with Ms Burton and her predecessor Eamon Gilmore "in the interests of the country and the interests of the people".
"I would like the opportunity to continue that in the time ahead," he added.
When the Tanaiste was asked whether she would consider working with Fianna Fail, Mr Kenny interjected: "You can't trust him. They talked before about temporary little arrangements with the PDs."
Source Irish Independent