The building in Warwickshire, which is used as a hotel and conference centre, has been sold to Firoka Group, a hotels business run by Tanzanian millionaire Firoz Kassam who also owns Oxford United Football Club.
Proceeds from the sale by PVH will be donated to the trust fund set up to aid former workers at MG Rover which went bust in April with debts of £1.4bn and the loss of 6,000 jobs at Longbridge.
The exact amount that will ultimately be transferred by PVH to the fund is not yet known because some charges will have to be deducted.
The castle, set in 28 acres of Warwickshire parkland, was one of the assets pledged by the Phoenix directors, led by John Towers, to a fund set up to help workers laid off after the collapse of MG Rover.
About 40 sealed bids were thought to have been received by the closing date in June and offers had been expected at about £5m.
Phoenix director Peter Beale says: "This sale is part of our process of disposing of all PVH assets to allow us to create value for the Longbridge Employee Trust.
"We are currently acting under legal advice not to transfer our shareholdings into the trust, but that advice is under constant review as the terms of reference and progress of the current DTI inquiry become clearer.
"In the light of recent press speculation to the contrary, we would like to take this opportunity of reassuring everyone that we remain completely committed to maximising the value of PVH assets and making this gift."
As well as Oxford United, Firoka Group also owns Heythrop Park, a 270-bed hotel set in 440 acres of the Oxfordshire countryside, as well as Holiday Inns in Kings Cross and Old Street in London.
The company last night said Studley would be getting a multi-million pound revamp.