PHOENIX, Ariz. — Nikola founder Trevor Milton has voluntarily stepped down as executive chairman and member of its board of directors, the company announced early Monday.

Nikola shares plunged nearly 30% in premarket trade on the news.

Milton’s resignation came less than two weeks after a short-selling firm accused him of lying about the potential of Nikola electric vehicles, hitting its stock hard.

Milton has been replaced by board member Stephen Girsky, former vice-chairman of General Motors.

Earlier this month GM took an 11% ownership stake in Nikola, after signing a strategic partnership to engineer and manufacture the Nikola Badger pickup truck.

“Nikola is truly in my blood and always will be, and the focus should be on the company and its world-changing mission, not me,” said Milton.

“So, I made the difficult decision to approach the board and volunteer to step aside as executive chairman.”

Girsky is a managing partner of VectoIQ, LLC, an independent advisory firm based in New York.

He has more than 30 years of experience working with corporate board executives, labor leaders, OEM leaders, suppliers, dealers and national policy makers.

Milton tweeted that he intends to defend himself against the “false allegations leveled against me by outside detractors”.