A Knight's Tale

At a jousting tournament in 14th-century Europe, young squires William Thatcher, Roland, and Wat discover that their master, Sir Ector, has died. If he had completed one final pass he would have won the tournament. Destitute, William wears Ector's armour to impersonate him, winning the tournament and taking the prize.
Although only nobles are allowed in tournaments, William is now inspired to compete and win more prizes. Roland and Wat would rather take their share of coins and leave, but William convinces them to stay and train him to joust. Along the way to his first tournament in Rouen, the trio encounters a young Geoffrey Chaucer, who is also destitute and agrees to forge the patent of nobility that will allow William to enter under the assumed name of "Sir Ulrich von Liechtenstein" from Gelderland. At the tournament, William is brought before Simon the Summoner and Peter the Pardoner: Chaucer has a gambling problem and is in their debt. William demands Chaucer be released and promises payment.
In the course of competition, William's armour is damaged. He goads Kate, a female blacksmith, to repair it without payment and goes on to win the sword event at the tournament. In the joust, he faces a Sir Thomas Colville, who withdraws from the tournament after being injured by William, though they exchange a ceremonial pass so that Colville can retain the honour of never having failed to complete a match. The proceedings are observed by Jocelyn, a noblewoman with whom William has become infatuated, and Count Adhemar, a rival both in the joust and for Jocelyn's heart. In the final joust of the tournament, Adhemar defeats William.
Kate joins William's party and forges new lightweight armour allowing him greater mobility. In the following tournament, Adhemar and William are both assigned to tilt against Sir Thomas Colville, but they learn that he is actually Edward, the Black Prince. Adhemar withdraws, but William continues the match and then addresses the prince by name, further earning Edward's respect.
Adhemar is called away to the battlefield, and William achieves several victories in his absence. William proves his love for Jocelyn by complying when she first asks him to deliberately lose (in contrast to the countless knights who promise to win in her name), and then, just before he would be eliminated, to win the tournament in her name after all.
The group travels to London for the World Championship. William recalls leaving his father to squire for Sir Ector and learn to become a knight hoping to "change his stars". Adhemar has also arrived in London and announces that he is in negotiations with Jocelyn's father for her hand in marriage. William dominates at the tournament and he returns to visit his father, now blind and living alone in Cheapside, but is discovered by Adhemar, who alerts the authorities to William's false identity.
William is placed in the pillory, but is defended from the hostile crowd by his friends. Just as the mob reaches its frenzy, Prince Edward emerges from the crowd, noting that his friends' dedication to him reflects an ability to inspire others that is in the best traditions of knighthood. In acknowledgement of William's honour, Edward announces that, William is in fact, "beyond contestation", descended from a noble lineage, and knights him "Sir William".
William returns to the tournament to face Adhemar in the final match, but Adhemar cheats with an illegal sharpened lance, piercing William's shoulder and seriously injuring him. Entering the final pass, William is losing by two lances and must unhorse Adhemar to win. He demands to be stripped of his armour while Chaucer buys time by performing the introduction of William that he omitted earlier. Finally he tilts against Adhemar, with his father and Jocelyn in attendance. Bellowing his true name as he tilts, he knocks Adhemar to the ground with a crushing blow. In the ensuing celebration, as Jocelyn and William embrace, Chaucer remarks that he should write this whole story down.

Question: Who defeats William in the final joust of the tournament?
Answer: Adhemar