DUBAI, Dec 20 (Reuters) - Commercial Bank of Qatar COMB.QA (CBQ), the Gulf Arab state's third-largest lender by assets, said on Tuesday that it had completed the acquisition of the outstanding 25 percent stake in Turkey's Alternatifbank for $224.9 million.

CBQ said in July that it would buy the stake after another shareholder, Turkey's Anadolu Industry Holding, an affiliate of Yazicilar Holding, exercised an option which required the Qatari bank to purchase the stock.

The deal means Alternatifbank is now a 100 percent-owned subsidiary of CBQ, according to Tuesday's bourse statement.

(Reporting by Tom Arnold; Editing by David French) ((Tom.Arnold@thomsonreuters.com; +97144536265; Reuters Messaging: tom.arnold.thomsonreuters.com@reuters.net))