This is the latest in a number of mergers we have seen in the independent schools sector in the past few years, the most recent being between Edgeborough prep school and Charterhouse.
Mill Hill has four campuses in the capital – Mill Hill School, Belmont, Grimsdell and Mill Hill International – offering co-education from ages three to 18.
The Mill Hill Schools Foundation said it selected Cobham Hall School for the merger as it has "a similar ethos of education; the opportunity to grow it further; the high quality of the school; and the relative proximity".
Parents have been told that the merger will not bring any key differences to the day to the day education at each school. Cobham Hall School and all four Mill Hill Schools will each keep the same leadership, branding, and school fees will remain the same.
Elliot Lipton, chair of governors at Mill Hill said: “This is a bringing together of like-minded schools that further strengthens the excellent education provided."
The Foundation told parents:
"The Foundation has seen significant recent growth in pupil numbers and has reached capacity in a number of areas, not least in boarding. The addition of Cobham Hall allows the Foundation to continue to increase pupil numbers but without adding further strain on existing facilities. The long history of the Foundation involves the development of new schools in the form of Belmont, Grimsdell and MMHI, allowing all the schools to thrive for generations to come."