Citron Research, a newsletter edited by Andrew Left that focuses on shorting opportunities, issued a formal apology Monday to three people criticized in a March commentary on Tesla (TSLA - Get Report) .

In the note Monday, Left wrote "On March 8, 2019, in an attempt to defend Tesla, Citron had a lapse in judgment and posted commentary that attacked the character and investment decisions of three intelligent and thoughtful people: David Einhorn, Jim Chanos, [and] Mark Spiegel."

Left went on "Both Mr. Einhorn and Mr. Chanos have always been men I have respected and I have grown to admire the perseverance of Mr. Spiegel."

In the March note, Left argued that critics of Elon Musk were being too hard on the Tesla founder and that the stock -- then trading at around $284 a share -- was poised for a rebound. Instead, Tesla shares went into a significant decline, trading as low as $176.99 by June. Shares have recovered somewhat over the summer and closed at $229.01 on Monday.

The March note specifically pointed out poor returns for fund managers Einhorn and Chanos, and said nobody had ever heard of Spiegel "until he started to dedicate his life to hating Tesla."

Reached by phone, Left told TheStreet, "I felt ashamed that I did it," adding "I think it came off as being mean spirited."

He said in 19 years of publishing his newsletter, this was the first apology he'd ever issued.

Left has been both long and short Tesla at different times, most recently turning positive on the stock last November as the company's Model 3 began shipping.

Chanos, a longtime Tesla bear, said as recently as June that the company's cars are poorly made and that Musk is relearning lessons about the car business, that Detroit learned 100 years ago.

Spiegel said in a tweet that he hadn't been bothered by the commentary:

I was never mad at Andrew Left (he called me "a nice and smart man"-- how mad could I be, lol?), plus the stock's down 20% since then, but to his credit he just posted this on his web site: https://t.co/M11aZ9t7VY$TSLA

— Mark B. Spiegel (@markbspiegel) August 12, 2019