The king is, well, not exactly dead. But Apple's stock has taken a pretty serious knee-capping this week, compounding a slide that began in September. And as a result, Exxon is once again king of the stock markets.

On Friday, Exxon became the world's most valuable company as Apple's stock fell in midday trading $10.46, or 2.32%, to $440.04.

In midday trading, Exxon boasted a $417.59 billion market cap; Apple's was $412.36 billion. The days of August, when people were debating whether Apple had set the record for the most valuable company in history, now seem like a dream from another era.

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Apple's stock has now dropped 37% since its September high of $702.10. In just the last two days, the stock is down 14.6%.

The question now facing Apple investors is just how far the stock can tumble before it reaches equilibrium.

While there has been a touch of schadenfreude as people watch analysts rein in bullish estimates and large Apple shareholders count their losses, it's worth noting that the company's stock is one of the most widely held in the world. It might be hard to find anyone with a pension fund or 401(k) who has not at least been affected a little by Apple's stock decline.