Andrew Lloyd Webber has sold four of his West End theatres to a consortium including former broadcasting executive Michael Grade.
Lord Lloyd-Webber said it had been a "gut wrenching decision" to sell off the Palace, Her Majesty's, the Cambridge and the New London theatres.
He said: "However following my illness last year I was advised to reduce the debt in the family company. It is particularly difficult for me as the New London was Cats' home for 21 years.
"For nearly 25 years Her Majesty's has been and still is the home of The Phantom of the Opera.
"The Palace has huge personal associations and was described by John Betjeman as 'the only theatre architecture ... which climbs into the regions of a work of art'.
"I am particularly proud that over the 25 years that I have owned the Palace I have been able to restore the magnificent auditorium and the exterior thereby removing the huge neon advertising hoarding that defaced both the theatre and Cambridge Circus."
The deal, which is expected to go through in January, leaves his company, The Really Useful Group, with the Palladium, the Theatre Royal Drury Lane and a 50% share in the Adelphi.
Lord Lloyd-Webber said the purchase price of the four theatres had been reduced by £5 million to allow that sum to be invested in their upkeep by their new owners.
Grade was born into a famous theatrical family. His father was theatrical agent Leslie Grade and his uncles were the impresarios Lew (later Lord) Grade, who ran ATV, and Bernard (later Lord) Delfont.