Tony Blair sent an affectionate handwritten letter to George Bush in praise of a "brilliant" speech to the UN in the lead up to the Iraq War.
The note was made public this morning as part of a cache of documents released with Sir John Chilcot's damning inquiry into the conflict.
The prime minister wrote that the US president's address to the UN General Assembly would help them "get the job done".
Mr Blair penned the note after Mr Bush had set out the case for war in the speech on September 12 2002, about six months before the invasion in March 2003.
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He wrote: "Dear George, it was a brilliant speech.
"It puts us on exactly the right strategy to get the job done.
"The reception has been very positive with everyone now challenged to come up to the mark. Well done.
"Yours ever, Tony."
The note's tone gives an indication of the warm personal relationship between the leaders, which is seen to have played a crucial role in the lead up to the war.
Mr Bush had told the UN that Saddam posed a "grave and gathering danger" and called on the UN act.
He warned that the first time the world would become certain that the dictator had of nuclear weapons could be when "he uses one".