Having worked at De Beers Jewellers for a decade, Delage will step down as CEO at the end of September.
Following his departure, Assimon will join the business on 1 September to “ensure a seamless transition of leadership”.
According to De Beers, Assimon has a “strong track record as a creative and inspirational leader”, with “extensive” global experience across marketing, sales and merchandising in the jewellery and luxury sector.
Prior to her appointment, she was worldwide head of high jewellery and high watchmaking Sales at Louis Vuitton, and later joined Piaget as its high jewellery and exceptional pieces director.
She has “successfully led” the commercial development of these brands, and was most recently CEO at luxury brand de Grisogono.
Stephen Lussier, chairman of De Beers Jewellers and Executive Vice President, Consumer & Brands at De Beers Group, said: “I’m really looking forward to Céline joining the business and leading it into its next phase of growth.
“As consumers increasingly seek out high quality and distinctive jewellery from leading luxury brands there is a great opportunity ahead, and Céline’s creative vision and outstanding expertise make her the ideal choice to help us capture it.”
He added: “I’d also like to thank François for his decade of service to De Beers Group and his contribution to our success over the years.
“As CEO firstly of Forevermark, and then of De Beers Jewellers, François has been a passionate leader with a love of diamonds and an uncompromising commitment to the beauty that distinguishes De Beers Group’s diamonds from those of other brands.”
Assimon said: “I am incredibly honoured to join De Beers Group and excited to begin writing the next chapter in De Beers Jewellers’ story. De Beers Jewellers holds tremendous potential as a trusted and creative high-end Maison.
“Together with the De Beers Jewellers team, I look forward to telling the story of our beautiful Maison and enchanting clients with our amazing creations.”