Over the past year, DoubleLine CEO Jeff Gundlach has been quite a vocal -- and correct -- Apple (NASDAQ:AAPL) bear. About a month ago, Gundlach started to change his tune, though. After shares plunged right through his call of $425 to bottom out near $385, the bond guru began to take more of a neutral stance primarily due to the Mac maker's rock-bottom valuation.

He wasn't exactly bullish when he discussed Apple's prospects a month ago, but he certainly couldn't be considered an Apple bear anymore, adding that he'd rather be long than short. Well, Gundlach is now an outright bull, and has initiated a long position in the iPhone maker.

Gundlach appeared on CNBC earlier this week, expressing confidence that Apple is heading to $500. Shares appear to be bottoming out, even if they have a hard time staying above $450. He notes that Apple is an "amazing study in market psychology," since sentiment has shifted so dramatically over the course of a year and the stock is now "reviled."

That pessimism may be overdone though, in his view, and he thinks the valuation multiples are too cheap to ignore, particularly when excluding its cash position. For reference, Apple now trades at 10.4 times earnings, and 6.8 times earnings excluding cash.

That's why Gundlach has been buying Apple at an average price under $425. Gundlach is also encouraged by Apple's ambitious new capital return program. Apple may never see prices of $700 again unless it enters new markets, he believes.

The good news for investors is that Apple is undoubtedly preparing to enter new markets. During the last conference call, Tim Cook teased that he's looking forward to "potential exciting new product categories," and during the D11 conference expressed confidence that Apple still has some more game changers in the works.

Gundlach was absolutely right with his bearish call. Will he be right now that he's siding with the bulls?

Fool contributor Evan Niu, CFA, owns shares of Apple. The Motley Fool recommends Apple. The Motley Fool owns shares of Apple. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.