Olivier Theyskens has quit as creative director of Theory.

The designer has opted to leave the fashion label after nearly four years at the helm of its creative output and will be succeeded by Theory's in-house design team.

Olivier thanked Theory chief executive officer Andrew Rosen for giving him an ''amazing opportunity'' to work for the brand.

He told WWD: ''It has been an amazing opportunity to work with Andrew and to benefit from his knowledge in this dynamic segment of fashion. I will always cherish our friendship.''

Olivier, who previously served as artistic director for Nina Ricci from 2007 to 2009, was initially hired to create a single collection for Theory, titled Theyskens' Theory. However, he was later permanently hired as the brand's creative director in 2011.

Theory CEO Andrew added: ''I am grateful for Olivier's extraordinary contribution to Theory over the past three-and-a-half years, and I am particularly excited to see what he does next. Everything has a life cycle.

''Olivier has done great work at Theory, and I believe his appointment at the company and his creativity within the studio enhanced the brand and added a new dimension and new possibilities to the market segment.''