The opposition has been filed to the UK Intellectual Property Office by Benjamin Worcester, who lives in Victoria, Australia, and is thought to have worked as an NHS doctor between 2011 and 2014, the World Trademark Review reports.
The reason why the Melbourne-based doctor has filed the notice has not yet been revealed, but the move could see Harry and Meghan enter a lengthy (and potentially costly) legal battle.
The couple first sought to register the Sussex Royal brand – which they have been using on their Instagram account since April 2019 – as a global trademark for a range of items and activities including clothing, stationery and the running of “emotional support groups” in June 2019.
However, all applications lead to an “opposition period” where anyone can object and file a complaint against the trademark.
The Duke and Duchess of Sussex’s period of opposition was due to end on 20 February 2020, but following the complaint from Dr Worcester, it has now been extended to 20 March 2020.
In this period more oppositions, or threats of opposition, could now be filed.
The trademark application follows an announcement made by the couple earlier this month stating their decision to step back as senior members of the royal family.
The move prompted the Queen to organise a crisis summit regarding Harry and Meghan’s future roles, where it was decided there would be a “period of transition” which will see them living in Canada and the UK.
In a statement, the Queen said that the royal family “respect and understand” their “desire to create a new life as a young family”.
Shortly after, Buckingham Palace issued an additional statement in which it stated that the couple would no longer receive public funding or be able to use their HRH titles.
“As agreed in this new arrangement, they understand that they are required to step back from royal duties, including official military appointments. They will no longer receive public funds for royal duties,” the statement read.
“The Sussexes will not use their HRH titles as they are no longer working members of the royal family."
The statement did not specify whether the Sussexes would be able to continue using the "royal" moniker if they were not working members of the royal family.