LONDON — Prince Harry and Meghan posted a final message on their Sussex Royal Instagram account on Monday before giving up their royal responsibilities.

On Tuesday, the couple will officially step down as working members of the British royal family. Although they will remain “the Duke and Duchess of Sussex,” they will no longer use their “royal highness” titles, and they will give up their “Sussex Royal” branding, letting their Instagram account and website go inactive.

“As we can all feel, the world at this moment seems extraordinarily fragile,” the couple wrote on Instagram. “Yet we are confident that every human being has the potential and opportunity to make a difference — as seen now across the globe, in our families, our communities and those on the front line — together we can lift each other up to realise the fullness of that promise.”

On Monday, palace officials announced separately that Harry’s father, Prince Charles, had concluded his period of ­self-isolation after testing positive for the novel coronavirus.

Harry and Meghan saw him, before he was diagnosed, when they did their final tour of duty in Britain this month.

The couple caught many by surprise — including, it appeared, Queen Elizabeth II, Harry’s grandmother — when they announced in January that they wanted to take on new roles and split their time between Britain and North America.

They initially moved with their young son, Archie, to the western Canadian province of British Columbia but have reportedly taken up residence in Los Angeles in recent days. The couple has neither confirmed nor denied those reports.

They plan to spend the coming months focused on family and their existing charities, according to a statement from a spokeswoman. But they are also launching a nonprofit focused on sustainable tourism.

“COVID-19 has presented the world with one of the greatest public health and socio-economic challenges of modern times,” read the statement. “It has also forced one of the biggest human behavioural changes in generations. When restrictions related to controlling the pandemic ease, the role of responsible tourism to support communities and destinations around the world will be more important than ever.

“The Duke is working closely with each of the Travalyst partners to better understand how this nonprofit organisation can aid in global recovery, especially by supporting communities, wildlife and the environment at the same time.”

The Sussexes and the royal family have agreed to review their situation in a year.

One of the more contentious issues about their departure has been over who will foot their security bill. On Sunday, President Trump tweeted that the U.S. government would not be picking up the tab.

The couple quickly fired back a statement saying that they had “no plans to ask the U.S. government for security resources” and that “privately funded security arrangements have been made.”