The last letter ever written by Mary Queen of Scots is to go on display for the first time in 30 years.

The 422-year-old manuscript - written six hours before her execution - will be one of the key exhibits unveiled by the National Library of Scotland later this month to mark the official launch of their new visitor centre.

Library bosses said the letter offers a once-in-a-lifetime opportunity to see a "fascinating piece" of history.

The priceless letter was written on February 8, 1587 to Henri III, King of France, the brother of her late husband Francois II.

It shows her belief that she died a religious martyr and not for purely political reasons, as the English government alleged.

And although just hours from death, the letter reveals that she even thinks of her servants and asks Henri to ensure their wages are paid.

Martyn Wade, chief executive of the National Library of Scotland in Edinburgh, said: "Written just six hours before her execution, the letter provides an incredible opportunity to see a fascinating piece of Scotland's history."

The letter was last seen in public 30 years ago.

Since then, the library's visitors have only been able to view a digitally-enhanced reproduction of the manuscript as it is stored under tightly-controlled conditions to prevent damage from heat, light and humidity.

For conservation reasons, the letter will be on display within a glass case for seven days only, beginning on Tuesday September 15.

It is not known when, or even if, the original will go on display again.

The precious manuscript will join ten other exhibits, which will remain on show until November 8.

The library's new visitor facilities are the result of a #2.24 million investment programme, undertaken over the last three years to make it more accessible.

Mr Wade, said: "The completion of the visitor centre marks an exciting new chapter for the National Library of Scotland.

"The Library is the home of the collected knowledge of Scotland, and the visitor centre gives people the opportunity to come in and find out just what that means.

"Three exhibition areas, a new shop and cafe plus an expanded events space and access to digital resources and wi-fi make the library more inviting than ever before."