Apple chief executive Tim Cook has thanked customers and employees as he prepares to leave the company’s top job in September, bringing his 15-year tenure as CEO towards a close.

In a letter to the Apple community published in April, Cook said he would remain at the company as executive chairman after handing the chief executive role to John Ternus, Apple’s senior vice-president of hardware engineering.

Cook described the leadership change as the next stage of his career at Apple and praised Ternus, a veteran of the company who has spent about 25 years working on its products.

Ternus has emerged as one of Apple’s most prominent executives through his leadership of hardware engineering. Under the planned management reshuffle, Johny Srouji is also taking over Ternus’s previous responsibilities and has been appointed chief hardware officer.

Cook used much of his letter to reflect on his relationship with Apple customers. He said he had regularly read messages from users describing how the company’s products had affected their lives, including stories involving Apple Watch health features, Macs, and other devices.

“This is not goodbye,” Cook wrote as he discussed the transition, thanking Apple users for their support during his time as chief executive.

Cook took over as Apple’s chief executive in 2011 following Steve Jobs. His tenure saw the company expand beyond its core iPhone and Mac businesses into areas including wearables and subscription services.

The transition will leave Ternus responsible for leading one of the world’s largest technology companies while Cook retains an influential position as executive chairman.

Cook expressed confidence in his successor, describing Ternus as an engineer with a strong understanding of Apple’s products, culture, and customers.

The planned September handover represents one of Apple’s most significant leadership changes since Cook himself succeeded Jobs, placing Ternus at the centre of the company’s next phase.