Prince Harry hit with fresh setback in the US

However, royal commentator Richard Eden said the charity has "fallen into trademark difficulties in the USA – thwarting, for now at least, plans to expand its operations in America."

Sentebale works with young people in Lesotho and Botswana to create sustainable solutions that address issues of health wealth and inequity.

Among the categories that Harry was hoping to trademark in his charity were “mental healthcare services,” “psychological and mental counselling services,” and “provision of immunisation.”

Also added to the list of categories was “organising of conferences, seminars, courses, workshops and other event,” and “production of audio and/or video recordings.”

Eden said: “But the US Patent and Trademark Office, while acknowledging that it has unearthed 'no conflicting [trade] marks', has given the application the thumbs-down.

“In a detailed ruling, it points out that many, if not quite all, the categories are inadequately defined.”

The duke must rectify the issues noted by the US Patent and Trademark Office and make a second attempt within six months.

The office said: “'An application must specify, in an explicit manner, the particular goods and services on or in connection with which the applicant uses, or has a bona fide intention to use, the [trade] mark in commerce.”

Moreover, accounts filed with the Charity Commission show that donations to the charity from the American Friends of Sentebale Foundation have halved in a year.

Donations have gone down from £1.2million to £610,000.

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It comes as Prince Harry has travelled to London to mark the 10th anniversary of the Invictus Games.

The prince is expected to be in the UK for just a few days before flying to Nigeria for an unofficial royal tour alongside his wife Meghan Markle later this month.

King Charles and his son Harry are not expected to meet due to “His Majesty’s full programme” whilst the prince is in the UK, according to a spokesperson for the duke.

No other senior members of the Royal Family are expected to attend the Invictus Games service held at St Paul’s Cathedral on Wednesday.