AOL's purchase of the Huffington Post closed Monday, and the same day, AOL's stock sank to its lowest price ever.

As noted by Business Insider's Chart of the Day, shares of AOL fell about 4%, or 79 cents, to $19.26 -- its lowest closing price so far. That was down about one-third from the one-year high it reached in April, Business Insider noted.

The decline in stock price may show a lack of investor confidence in Chief Executive Tim Armstrong's attempt to turn AOL around. Much of that plan is pinned on the combined vision of Armstong and Arianna Huffington, who is becoming president and editor in chief of a new Huffington Post Media Group inside AOL.

AOL, looking to capitalize on the success of the Huffington Post website and brand, is putting the majority of its online publishing properties under Huffington's control.

AOL announced February 6 that it was buying the Huffington Post for $315 million.

Last month, Armstrong personally bought $10 million in AOL stock, possibly to breed confidence in his plan to return AOL to leadership standing in the tech industry. Under Armstrong, AOL has launched a redesign of AOL.com and bought the technology blog TechCrunch.

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-- Nathan Olivarez-Giles

twitter.com/nateog