Apple’s chief operating officer plans to hand the role off this month and retire later this year after roughly a decade as the tech giant’s No. 2 under Chief Executive Tim Cook.

Cook will directly oversee Apple’s design starting later this year, just as its software interfaces unify under the new Liquid Glass approach.

The transition does raise fresh questions about Apple’s CEO succession plan. Williams became COO in 2015, and because Tim Cook became chief executive through that route, speculation regarding Williams as a successor began to bubble up.