The King sipped a ceremonial drink and was presented with a pig for feasting during a first day of events in Samoa.
The monarch was “dressed down”, allowing a red garland to be placed around his neck as he was honoured with a new title.
He was in good spirits despite the rain and clutched a bamboo-handled umbrella as he met locals.
The 75-year-old took part in a traditional ‘ava ceremony, with the drink prepared by the daughter of Samoa’s head of state.
As is custom, the King poured a few drops away before drinking deeply from a cup made of coconut shell.
He was wearing a short-sleeved white “Royal Navy”-style bush jacket and trousers he designed himself as he was honoured.
The jacket, similar to an elei, a smart casual short-sleeved shirt worn by Samoan men, was made by Anderson & Shepperd and featured fabric trim by the Samoan School of Arts.
The ceremony took place at the Pacific island’s national university in a falesamoa, a large open-air covered hall made from timber.
A garland of dried fruit from the pandanus tree was placed around the King’s neck, while the Queen was given a floral arrangement.
They were also given a selection of gifts, including a pig carcass for feasting.
The ceremony was watched by village elders and dignitaries including Samoan Prime Afioga Fiame Naomi Mata’afa and Foreign Secretary David Lammy.
The royals’ stay in Samoa follows their brief tour of Australia earlier this week when a senator controversially heckled the King in parliament.