Their arrival in Fiji's capital of Suva on Tuesday will be followed by two days of engagements focused on the environment and education before the Duke and Duchess of Sussex head to Tonga.

It has been a jam-packed trip so far for the newlyweds, who revealed the ultimate surprise when they announced their pregnancy upon landing in Sydney.

After a gruelling week of engagements, the duchess cut back on some planned appearances on Sunday so she could rest.

However, she bounced back on Monday to join the duke on Queensland's Fraser Island.

Meghan spent most of the day at a luxury resort, avoiding the bumpy terrain Harry needed to traverse on the world's largest sand island to carry out his official engagements.

Harry was there to unveil a plaque adding the holiday destination's 83,757 hectares of pristine rainforests to the Queen's Commonwealth Canopy project.

He went barefoot in the sacred waters of Lake McKenzie and was briefed by Butchulla elders about the ancestral significance of various sites across the island, known as K'gari.

"I think he was blown away ... the size of the timbers we took him to, the beauty of the lakes, you know, talking with our songman, our rangers, and hearing it from both points of view on things he had not thought about," Aunty Nai Nai said.

Land and sea rangers and dancers who met the duke told of a mutual respect, acknowledging the significance of his visit to their land and new understanding of traditional Butchulla practices.

The royal couple later reunited for an afternoon stroll along the island's Kingfisher Bay jetty, delighting locals.

The duchess is expected to be by her husband's side at all their planned engagements in Fiji and Tonga.

In the meantime, Harry's Invictus Games for wounded defence veterans continues in Sydney.

The duke and duchess are expected to catch some of the final events when they return to the harbour city on Friday.

They are due to jet off to New Zealand on Sunday for the last stops on their 16-day tour.

Australian Associated Press