In 1923, after the demise of the Cornwallis-West family, The Castle was sold to become an eminent international private clinic for the investigation and treatment of obscure medical diseases, but was subsequently closed around 1950.
In the early 1960’s The Castle was purchased at auction and converted into an hotel. One of its most notable guests since was HRH Prince Charles who stayed on his way to his investiture as Prince of Wales (the 21st Prince of Wales since the new title began in 1301).
In 2004, Ruthin Castle was purchased by Anthony and Amanda Saint Claire. The Saint Claire family fight to conserve the overall property with some assistance from the Welsh Government Tourism Investment Scheme, and have expended more than £4million on the repair, development and refurbishment of the property in that time, including bringing large decayed and outdated portions of the interior back into use.