Andrew Lloyd Webber is donating £3.5 million to refurbish an arts school whose former pupils include Catherine Zeta Jones and Martin Clunes.
The money will be ploughed into overhauling the auditorium, building costume storage facilities, soundproof studios and editing rooms, as well as improving facilities for disabled students.
The fee-paying Arts Educational Schools, in Chiswick in west London, provide an arts-based education for 11 to 18-year-olds, and teach undergraduate and part-time courses.
The Andrew Lloyd Webber Foundation awards 10 musical theatre scholarships every year for students to attend performing arts training institutions such as the Arts Educational Schools London.
The theatre impresario said: "I am delighted the foundation is able to make such a substantial donation to fund the refurbishment of the Arts Educational Schools.
"The new facilities will provide an ideal environment for the students to take advantage of the exemplary training the School is renowned for.
"I have been a supporter of Arts Educational Schools for many years and I am very excited that the Foundation can make a real difference to the students who will be future stars of stage and screen."
The institution's alumni also include Jane Seymour, Julie Andrews, Cherie Lunghi, Nigel Harman, Will Young and Nigel Havers.