Just four days after Nvidia Corp.'s board publicly expressed confidence in Jensen Huang, the co-founder who built the company into a $4 trillion AI giant was gone.

Nvidia announced Thursday that Huang had resigned as president, chief executive and a member of the board, effective immediately. Chief Financial Officer Colette Kress was named interim CEO, and longtime director Harvey C. Jones became the company's first board chair.

The speed of the exit stunned investors. On Sunday, the board said it had confidence in Huang and his leadership team. By Wednesday night, it had accepted his resignation, according to a regulatory filing.

Nvidia has not given a reason for the resignation. Its filing with the Securities and Exchange Commission describes no disagreement between Huang and the board. The company thanked Huang "for his immeasurable contributions to the company and the industry."

Based on reporting and analyst commentary, here are five possible reasons the end came so quickly.

1. A second relationship, this time with a direct report

The turning point appears to have come Wednesday afternoon. The New York Times reported that Huang had an extramarital relationship with Kimberly Powell, Nvidia's vice president of health care, who reported directly to him.

That report changed the nature of the scandal. Huang's earlier admitted affair involved Alice Huang, an executive at an outside company. A relationship with a subordinate raises questions about workplace........

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