An internet search of 5-10 seconds will lead you to the poem, "Morte d'Arthur", by Alfred Lord Tennyson.
It later became part of his work by the name of, "Idylls of the King", and it is Tennyson's description of certain chapters of Sir Thomas Malory's work by the same name. However, make no mistake about it; Alfred Lord Tennyson most certainly wrote a poem by the name of "Mort d'Arthur"; it was published under that name in 1842. ("Idylls of the King" was published in 1759.)
Should be 1859, but I'm sure you spotted the typo.