Twitter shareholders sold out for a princely sum.

Saudi Prince Alwaleed bin Talal pumped $300 million into the pockets of existing Twitter investors when he bought a roughly 4 percent stake in the micro-blogging service.

The prince’s Kingdom Holdings reportedly participated in a secondary offering, which allows early investors to cash out, rather than injecting new money into the company.

The firm disclosed the deal yesterday, although it was part of an earlier $800 million fundraising round Twitter closed in September that valued it at around $8 billion.

The prince also has made big investments in blue-chip companies such as Citigroup, Apple, Time Warner and News Corp., which own The Post.

The investment follows Twitter’s high-profile role in the Arab Spring that swept away Middle Eastern dictatorships in popular uprisings.

Prince Alwaleed, who is seen as a moderate in the Saudi kingdom, was quick to stress yesterday that the investment was not politically motivated and does not give him voting control.