A copy of an unknown Robert the Bruce letter from the build-up to the Battle of Bannockburn has been discovered.
The letter, sent in 1310, asks English King Edward II to stop persecuting the Scots.
It shows Robert asserting his God-given authority as king of the Scots and addressing Edward as his equal.
The script, thought to have been transcribed from the original, was discovered by chance by a professor of Scottish history at Glasgow University.
Bruce's Scottish troops defeated the English army at the Battle of Bannockburn in 1314.
The new letter was found in a document which dates from about the turn of the 16th Century and has presented historians with fresh information about a pivotal time in the wars of Scottish independence.
The missive reveals how Robert made an appeal for peace when faced with an English army marching into the heart of Scotland but on the understanding that Edward would recognise Scottish independence.
King Edward was growing increasingly unpopular with the nobles in his own court, according to historians, while Robert was slowly reclaiming power north of the border by winning the hearts and minds of the Scottish people.
Prof Dauvit Broun, who made the discovery at the British Library, said: "The letter reveals a couple of things. Firstly, Bruce's tone is extremely conciliatory. He seems to be offering to do anything possible to establish peace. However, he is nonetheless plainly addressing Edward as one king to another.
"There is no doubt that the bottom line here is that Edward should recognise Robert as king of the Scots, and the Scots as separate from the English."
He added: "The writing of this letter should be seen as a bold move by Bruce who had perhaps recognised that the tables were turning and he could stand his ground in the face of an advancing English army and open negotiations with the king."
The letter, translated from its original Latin, states: "To the most serene prince the lord Edward by God's grace illustrious king of England, (from) Robert by the same grace king of Scots."
It adds: "Our humbleness has led us, now and at other times, to beseech your highness more devoutly so that, having God and public decency in sight, you would take pains to cease from our persecution and the disturbance of the people of our kingdom in order that devastation and the spilling of a neighbour's blood may henceforth stop."
By the time of the Battle of Bannockburn in 1314, Bruce had taken all the strongholds except Stirling and those near the English border.
In the end, Bruce's move in 1310 paid off as King Edward took his army south again to Berwick where he remained until July the next year.
The next time he returned north, three years later, Edward was beaten at Bannockburn.
Preparations are under way in Scotland to commemorate the 700th anniversary of the decisive Battle of Bannockburn next year.