Some British and Australian media outlets had questioned whether the trip would take place at all in the weeks that followed news of the King's cancer diagnosis, which was made public on February 5.
The palace confirmed that Charles and Camilla will attend the Commonwealth Heads of Government Meeting in Samoa, scheduled to take place between October 21-25.
The tour will not extend to New Zealand, however, as had been planned initially.
"The King's doctors have advised that such an extended programme should be avoided at this time, to prioritise His Majesty's continued recovery," a Buckingham Palace spokesperson said.
The programmes in Australia and Samoa would be subject to doctors' advice and could be modified accordingly, the palace said.
Buckingham Palace also published new portraits of the King and Queen on Sunday, wearing Australian and New Zealand decorations and insignia.
The 75-year-old King returned to public duties at the end of April for the first time since his diagnosis for an unspecified form of cancer. Buckingham Palace said that his diary would be managed carefully to minimise any health risks.
