DETROIT — Stellantis CEO Antonio Filosa has said leading the transatlantic automaker is a dream come true, but the company's stock has been anything but that for investors under his short tenure thus far.

Stellantis stock is off nearly 30% since Filosa, a company veteran from Italy who climbed through the ranks, was named CEO nearly a year ago. It's down about 21% since he officially started as CEO last June.

Tune in Thursday, May 21, at 10:25 a.m. ET: CNBC's Phil LeBeau interviews Stellantis CEO Antonio Filosa. Watch in real time on CNBC+ or the CNBC Pro stream.

Thursday marks a major next step for Filosa and his executive team, as they unveil a turnaround plan for the embattled automaker during a capital markets day at Stellantis' North American headquarters near Detroit.

Filosa has promised investors that the day "will outline the next phase of our strategy with clear priorities, clear targets, and a focused road map for execution."

The strategy he and others will present this week is expected to focus regionally on key brands such as Jeep and Ram in the U.S. and Fiat and Peugeot in Europe, detail how they plan to reduce costs and lay out how the company aims to return to profitability following a net loss of 22.3 billion euros ($26.3 billion) last year.

"It was my dream to take the helm of Stellantis … but obviously I recognized, at the time, with my team, that there were still things to be fixed," Filosa said during a Financial Times event last week. "We are fixing them at the speed of light, and I truly believe that now, and we will share that May 21 at our investor day, we have a clear path of sustainable and comfortable growth in front of us."