'Long stood Sir Bedivere

Revolving many memories, till the hull 

Looked one black dot against the verge of dawn,

And on the mere

the wailing died away.'

Alfred, Lord Tennyson. The Idylls of the King Part 12

After being seriously wounded,

 by Mordred, 

at the Battle of Camlann,  

Arthur was carried off to the Isle of Avalon for healing.

Leaving his faithful companion, 

Bedivere, 

to mourn his passing.