The White Knight

I read a short story in high school that I can't get it out of my head, but neither can I find the original story. If you know who it's by or what it's called, please leave a comment. It goes like this:

There was a young, brave knight who wanted to go out and bring truth, justice and happiness to all. He wanted to put a stop to all that would prevent this, namely the black knights. One day he was done all his training, all his gear was in sparkly, shinning white, working order and he set out. It was not long before he saw in the distance a blank knight cresting a hill. The black knight raised his weapon in challenge. The white knight bravely raised his as well and charged the black knight and won. That was the first of many victories.

After many years and many victories the white knight became tired. In the many battles that he had fought for truth, justice and freedom his armor had become dented, tarnished and scored. It had become the colour of soot from the flames of the dragons he had slain. He decided at long last to return home.

As he neared home he crested one of the last hills. In the distance he sees a white knight, with new shinny amour. He feels glad to see a friendly face after so long so he raises his weapon in greeting. The young white knight also raises his weapon. Then the young white knight charges.

Update: Austin Repath left a comment explaining that it was a story by Eric Nicol and even provided a link.

Update Again: Since I'd like a record of this story and don't trust that the other link will stay up indefinally, below is the story copied from the page. 

The White Knight

by Eric Nicol

Once upon a time there was a knight who lived in a little castle on the edge of the forest of life. One day he looked in the mirror and saw that he was a White Knight.  "Lo," he cried, "I am a White Knight and therefore represent good.  I am the champion of virtue and honour and justice and I must ride into the forest and slay the Black Knight who is evil."
    So the White Knight mounted his snow white steed and rode off into forest to find the Black Knight and slay him in single combat.  Many miles he rode the first day, without so much as a glimpse of the Black Knight.  The second day he rode even further, still without sighting the ebony armour of mischief.  Day after day he rode, deeper and deeper into the forest of Life, searching thicket and gulley and even the tree tops.  The Black Knight was nowhere to be found.
    Yet the White Knight found many signs of the Black Knights presence.  Again and again he passed villages where the Black Knight had struck – a baker's shop robbed, a horse stolen, an innkeepers' daughter ravished.  But always he just missed catching the doer of these deeds.
    At last the White Knight had spent all of his gold in the cause of his search.  He was tired and hungry.  Feeling his strength ebbing he was forced to steal some buns from a bakeshop. His horse went lame, so he had to replace silently and at night with another man's horse. And when he stumbled faint and exhausted into an inn, the innkeeper's daughter gave him her bed and because he was the White Knight in shining armour she gave him her love. But when he was strong enough to leave the inn, she cried bitterly because she could not understand that he had to go and find the Black Knight and slay him.
    Through many months, under hot sun and over frosty paths, the White Knight pressed on in his search, yet all the knights he met in the forest were, like himself, fairly white, depending on how long they, too, had been searching. There were knight of varying shades of whiteness depending on how long they, too had been hunting the Black Knight.
    Some were sparkling white. These had just started hunting that same day and they irritated the White Knight by innocently asking the way to the nearest Black Knight. Others were tattle-tale grey. And others were so grubby, horse and rider that the mirror in their castle would never have recognized them.
    Yet the White Knight was shocked the day a knight of gleaming whiteness confronted him suddenly in the forest and with a wild whoop thundered towards him with leveled lance.  The White Knight barely had time to draw his own sword and ducking under the deadly steel plunge his blade into the attacker's breast.
    The White Knight dismounted and kneeled beside his mortally wounded assailant, whose visor had fallen back to reveal blond curls and a youthful face. He heard the words , whispered in anguish, "Is evil then triumphant?"  And holding the dead knight in his arms he saw that beside the bright armour of the youth his own besmirched by the long quest, looked black in the darkness of the forest.
    His heart heavy with horror and grief, the White Knight who was white no more, buried the boy, then slowly stripped off his own soiled armour, turned his grimy horse free to the forest and stood naked and alone in the quiet dusk.
    Before him lay a path which he slowly took that led him back to his castle and closed the door behind him.  He went to the mirror and saw that it no more gave back the image of the White Knight, but only that of a middle aged naked man, a man who had stolen and ravished and killed in pursuit of evil.
    Thereafter when he walked abroad from his castle he wore a coat of simple colours, a cheerful motley and never looked for more than he could see.  And his hair grew slowly white as did his find full beard, and the people all around called him the good white knight.
From a high school anthology called And Who Are You?, edited by Austin Repath.