Akzo Nobel NV (AKZOY) said Wednesday that its CEO, Ton Buchner, will step down immediately due to health concerns.

Buchner, who has led the group since 2012, will be replaced by Thierry Vanlancker, who has been running the group's Speciality Chemicals business, a unit which could be separated as part of a broader strategic review the company announced earlier this year. A new head of the Speciality Chemicals business will be named in due course, the company said.

"It is with great regret that Ton is stepping down due to health reasons," said chairman Antony Burgmans. "He has been an outstanding leader for AkzoNobel, transforming the company and setting it up for future success. His focus on delivering for our customers and operational excellence has driven profitability to record levels, increasing returns to shareholders."

The change in leadership follows a months-long battle with activist investor Elliott Advisors (UK), the British subsidiary of Elliott Management and owner of a 9.5% stake in Akzo Nobel, which continues to push for the ouster of Burgmans and major changes in its management team.

AkzoNobel turned away three separate approaches from PPG Industries Inc. (PPG - Get Report) , favoring instead its own strategic review, which it says is a "superior route to growth and long-term value creation." Those plans include splitting the paints and coatings business from its speciality chemicals group within 12 months and returning the majority of sale proceeds to shareholders. PPG dropped its last $29 billion bid in June.

Akzo shares were marked 0.21% higher at €78.01 in early Amsterdam trading Wednesday, extending their gain to around 21.2% since news of PPG's approach was first revealed in early March.