Saudi Prince Alwaleed Bin Talal today announced that he has invested $300 million in Twitter, via his Kingdom Holding investment group.

Fortune has learned that the deal is structured as a secondary, which means that Alwaleed purchased shares from existing Twitter insiders. The company would have been required to approve of the transaction, but will not actually receive any of the $300 million, as it would in a more traditional investment.

Earlier this year, Twitter completed an $800 million funding round that included a $400 million direct investment and a $400 million secondary component. It is unclear if Prince Alwaleed’s investment is part of that transaction. [Update: TechCrunch reports that this $300m was part of that $800m deal.]

Twitter has raised over $750 million in direct venture capital, from firms like Spark Capital, Union Square Ventures, Kleiner Perkins, Benchmark Capital, Institutional Venture Partners, T. Rowe Price and DST Group. It is unclear which of these firms — or other company insiders, such as current or past employees — sold shares to Prince Alwaleed.

Twitter declined to comment.

Update: I did a CNBC phoner about this story. Watch below:

[cnnmoney-cnbc vid=http://video.cnbc.com/gallery/?video=3000063207]

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