Foreign Secretary William Hague said he was "very sad" to hear of the death of Saudi Arabia's Crown Prince Nayef as he sent his condolences to the kingdom.
Mr Hague said Prince Nayef, who was also deputy prime minister, served with "great dignity and dedication" and would be remembered for his contribution to the nation's prosperity and security.
The Saudi royal family said he died in an overseas hospital but did not specify where and confirmed he would be buried on Sunday after prayers.
Prince Nayef was elevated to the title in November 2011 after the death of his brother Sultan and a new crown prince will now be chosen from among his brothers and half-brothers.
Mr Hague said: "He served the kingdom for many years with great dignity and dedication and his contribution to the prosperity and security of the Kingdom will be long remembered.