No Worries, Sergey. We Can Make It Back in a Week on Mesothelioma Ads.

When Google took a five percent stake in AOL for $1 billion in 2005, it valued the company at about $20 billion. Last year the search giant wrote down $726 million of that investment.

Now, according to a regulatory filing, Google (GOOG) has gone and sold its share back to Time Warner (TWX) for $283 million, about a quarter of what it originally paid. Which means that in four years, AOL’s value has declined from an estimated $20 billion to an estimated $5.7 billion.

What an amazing loss of value.

According to the filing, AOL, which will be spun off by Time Warner later this year, made $678 million of the $2 billion in advertising revenue it collected in 2008 from its search advertising partnership with Google. Quite a chunk. AOL CEO Tim Armstrong best hope he’s able to renew that partnership when it expires at the end of 2010.