In January 1962 Rolls-Royce and BMC announced a technical collaboration initially to produce a new Bentley model using an existing BMC body, codenamed Java. A Princess 3 Litre Mark II was sent to Crewe in January 1962.

Known as experimental 71-B the car was fitted with a Rolls-Royce F-60 aluminium 6-cylinder engine and Rolls automatic gearbox. Modifications were made to its steering and brakes. Another BMC 3-litre body was sent to Crewe in late 1962. This body was altered externally with the fitting of a Bentley radiator grille, stacked headlights and modifications to the rear wings as shown in the photos. This car was known as experimental 72-B. With the Java project being cancelled car 72-B was scrapped at Crewe in January 1963. Car 71-B remained as a test vehicle but was scrapped in late 1965.

During the time of the Java project, Vanden Plas had also been busy with ideas on updating the Princess 3 Litre. In August 1964 the Vanden Plas Princess 4 Litre R was introduced to replace the 3 Litre Mark II. The new car was widely acclaimed and BMC had hopes of selling in excess of 100 units per week. The basic design, style and structure was similar to the earlier car, however the body was reworked with a new roof panel giving extra headroom and the elimination of the peaks over the front and rear screens. The rear end was smoothed out with the fins of the 3 litre all but disappearing. Horizontal rear light clusters were fitted and considerable extra stiffness was achieved at the back by making the rear panel part of the main structure. This did however mean that the bootlid no longer opened to bumper level. At the front new side/flasher units were fitted and the foglights were recessed into the front panel rather than being bolted to the front bumper as on the 3 Litre.

Mechanically the car was fitted with a Rolls-Royce FB60 4 Litre engine with output of 175bhp at 4800rpm. Having an alloy block this engine was lighter than the old BMC 'C' series 3 litre engine. For the first time on a British car, Borg-Warner type D8 automatic transmission was fitted as standard. A new Cam Gears Hydrosteer power-steering unit was also standard equipment.

Internally differences to the Princess 3 Litre were a slightly re-designed facia with safety padding all round, soft sunvisors and a rear heater as standard. 

Only one estate/Countryman was produced by Vanden Plas and that was to replace the earlier 3 Litre Countryman for H.M. The Queen. At least 2 estates were produced by the firm of Harold Radford (Coachbuilders) Ltd., by converting customers 4 Litre R saloons. 

Unfortunately various unreliability problems dogged the 4 Litre R and after an initial surge, sales declined to a trickle until the model was dropped in 1968. Only 6,687 vehicles were made at Kingsbury plus an additional 312 C.K.D. kits shipped to South Africa making a total of 6,999 in total.