It is part of an exhibition on the shepherd and writer from Trawsfynydd in Gwynedd who died in World War I.
In it he describes life “behind the lines” of the Western Front.
Handwritten “from somewhere in France”, the letter does not reveal the horrors of the trenches but focuses on what the university describes as “small moments of beauty” around him such as trees and flowers.
He also writes that France’s flowers “will be doleful in the future and a sad wind will blow over her acres because the colour of blood will be in one and the sound of sorrow will be in another”.
“(It) almost predicts the symbolism of the Remembrance Day poppy,” said a university spokesperson.
Professor Gerwyn Williams, head of the university’s school of Welsh, said the letter offered a “direct and unique connection with the poet”.
“It’s an excellent example of the treasures to be found at Bangor University’s archive, a rare manuscript which brings to life the experience of studying the work of an important man of letters,” he said.
Hedd Wyn was one of more than 8,500 soldiers, sailors and airmen from north Wales who died in World War I.
He was awarded the eisteddfod chair in Birkenhead and is still the only person to have won one of the festival’s major awards after their death.
A film about his life was nominated for a foreign language Oscar in 1994.
The exhibition at the Shankland Reading Room in the university’s main arts library can be viewed seven days a week.
Just after Pilkem is a cross roads, and located on the wall of a brick building oposite De Sportman bar is a plaque to Hedd Wyn. Hedd Wyn’s real name was Ellis Humphrey Evans, and he served as a Private in the 15th Battalion of the Royal Welsh Fusiliers.
The plaque gives more information in three languages: Welsh, English and Flemish. It states that Evans was mortally wounded near this cross-roads on the 31st of July 1917. Just over a month later he was awarded, post-humously, the major Welsh poetry prize – the Chair of the National Eisteddfod. He is buried west of here at Artillery Wood Cemetery in Boesinghe. The plaque was erected on the 31st of July 1992.
Robert Graves met him once,
in the hills above Harlech,
the shepherd poet,
the awdl and the englyn in his blood
like the heft of the mountain
in the breeding of his flock.
In a letter from France, he writes
of poplars whispering, the sun going down
among the foliage like an angel of fire,
and flowers half hidden in leaves
growing in a spent shell.
‘Beauty is stronger than war.’
Yet he heard sorrow in the wind, foretold
blood in the rain reddening the fields
under the shadow of crows,
till he fell to his knees at Passchendaele,
grasping two fists-full of earth, a shell to the stomach
opening its scarlet blossom.
At the Eisteddfod they called his name three times,
his audience waiting to rise, thrilled,
to crown him, chair him,
to sing the hymn of peace,
not ‘the festival in tears and the poet in his grave’,
a black sheet placed across the empty chair.