Their plans will be mixed with a little fun as Harry and Meghan will cuddle with koalas and joeys at the Taronga Zoo in Sydney before travelling to Tonga to have a dinner with King Tupou VI and Queen Nanasipau'u.
It all begins on Tuesday when the couple will meet Govenor-General Sir Peter Cosgrove and his wife Lady Cosgrove at Admiralty House.
They were said to have been greeted by a heavy police presence at Sydney Airport before making their way to Admiralty House, the Governor-General's Sydney residence.
The trip, their first outside the United Kingdom and Ireland, will officially begin on Tuesday and will see the couple watch the Invictus Games, visit a Sydney zoo and visit the rural Flying Doctor service.
The couple will attend the games' launch and closing ceremonies.
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Last May he said that Patisserie Valerie had "a strong balance sheet" so the problems will come as a major disappointment to him. Mr Johnson said: "We are all deeply concerned about this news and the potential impact on the business".
They will be in Australia for a total of nine days, where they will open the Invictus Games in Sydney on October 20 and attend a number of other events including public picnics, farm visits and "Fluoro Day" for mental health.
Just weeks ago the palace revealed the royal couple's full itinerary, setting out every detail of their visits to New South Wales, Queensland and Victoria, before they go on a visit to Fiji, Tonga and New Zealand.
The duke and duchess will learn about environmental challenges while in Wellington, visit a charity which supports children with parents in prison, and meet members of the public in Auckland and Rotura.
Mulroney likely provided her expertise for Markle's engagement party last November, and might have also been behind the beige trench coat from House of Nonie that the Duchess of Sussex wore to the Nelson Mandela Centenary Exhibit in London in July.
Kensington Palace said: "There is a long history of friendship between the Royal Family and Australia, Fiji, Tonga and New Zealand, and their links with the United Kingdom are extensive".