Lancelot had one failing, his adultorous love of Queen Guinevere. They tried to keep this love secret, it became known, and eventually brought about the undoing of the Round Table.
Lancelot and Guinevere's love for each other grew slowly. Initially Guinevere kept Lancelot away from her. Eventually, however the pair became lovers. Sir Meliagaunt grew suspicious and confronted Sir Lancelot in front of both the king and queen. The "insult" led to single combat between the two, in order to reveal the truth. Sir Lancelot overpowered Sir Meliagaunt, and cleaved his head into in two bits. Sir Lancelot and Queen Guinevere's honour were restored.
Sir Meliaguant was not the only knight suspicious of the pair's relationship. Sir Agravain and Sir Modred, King Arthur's nephew, led a band of 12 knights to Guinevere's chamber where they disturbed the lovers in bed. Sir Lancelot his escape by fighting his way out of the castle, but Guinevere was seized and condemned to burn to death for her adultery. Sir Lancelot returned several days later to rescue his Guinevere, killing several of King Arthur's knights in the process
King Arthur later attacked Lancelot's castle without success. Lancelot ended his days as a hermit and Guinevere became a nun at Amesbury where she died.
Like souls that balance joy and pain,
With tears and smiles from heaven again
The maiden Spring upon the plain
Came in a sunlit fall of rain.
In crystal vapor everywhere
Blue isles of heaven laugh'd between,
And far, in forest-deeps unseen,
The topmost elm-tree gather'd green
From draughts of balmy air.
Sometimes the linnet piped his song;
Sometimes the throstle whistled strong;
Sometimes the sparhawk, wheel'd along,
Hush'd all the groves from fear of wrong;
By grassy capes with fuller sound
In curves the yellowing river ran,
And drooping chestnut-buds began
To spread into the perfect fan,
Above the teeming ground.
Then, in the boyhood of the year,
Sir Launcelot and Queen Guinevere
Rode thro' the coverts of the deer,
With blissful treble ringing clear.
She seem'd a part of joyous Spring;
A gown of grass-green silk she wore,
Buckled with golden clasps before;
A light-green tuft of plumes she bore
Closed in a golden ring.
Now on some twisted ivy-net,
Now by some tinkling rivulet,
In mosses mixt with violet
Her cream-white mule his pastern set;
And fleeter now she skimm'd the plains
Than she whose elfin prancer springs
By night to eery warblings,
When all the glimmering moorland rings
With jingling bridle-reins.
As she fled fast thro' sun and shade,
The happy winds upon her play'd,
Blowing the ringlet from the braid.
She look'd so lovely, as she sway'd
The rein with dainty finger-tips,
A man had given all other bliss,
And all his worldly worth for this,
To waste his whole heart in one kiss
Upon her perfect lips.
Sir Lancelot, knight of the Round Table