Citadel, the Chicago hedge fund led by billionaire financier Kenneth Griffin, has filed documents with the SEC disclosing that it owns 6.1 percent of Seattle online real estate company Zillow.

The filing comes as Zillow’s stock continues to slump, though it is up nearly three percent in trading today at about $26 per share. The stock is down more than 35 percent in the past six months, after a spectacular run on Wall Street in which it at one topped $45 per share.

Citadel is one of the largest hedge funds in the world, and Griffin is estimated to be worth $3.1 billion, according to Forbes.

“In every business relationship, Citadel strives to be a trusted partner,” the firm writes on its Web site. “We move to wherever opportunity exists, bringing our clients and partners with us.”

According to the SEC filing, Citadel now owns 1,588,436 shares of Zillow’s class A stock. That’s up from 442,775 shares earlier this year.

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