Prince Harry and Meghan Markle are trying to rival the Royal Family in order to save their popularity, a royal expert has claimed.

The Duke and Duchess of Sussex recently embarked on a three-day trip to Nigeria, dubbed 'unofficial royal tour' by many, to promote mental health for soldiers and empower young people.

Now a royal expert has claimed that there is an 'alternate' Montecito Royal Family 'emerging' across the pond.

Royal author and historian Gareth Russell told the Sun: "To all intents and purposes that [an alternate royal family] is a real possibility.

"The problem for the Sussexes is that once you start doing anything like that, people become a lot more critical of what you do outside that - like commercial endeavours or quasi-royal tours."

The expert stated that the Sussexes' latest move will put them "under more of a microscope because they're calling it 'The Office of Harry and Meghan'."

He questioned whether the move was part of the couple's plan to break away from various harsh headlines they've had over the past few years after attacking the royals.

Mr Russell said: "Is it maybe a slightly more socially conservative direction and have themselves as royals in exile for want of a better word? I wonder is that them acting on advice that people don't want to hear them criticising the Royal Family."

He also claimed the pair could be on their way for more 'faux-royal tours' in the future.

He stated: "Their popularity at the moment is pretty low in America but that could change. Public opinion is always a bit of a rollercoaster.

"But they absolutely could (go on a US tour) and there are indications that they will."

It comes as a recent poll by YouGov revealed the Montecito pair remain the least popular royal couple.

According to the survey, of the two, Meghan Markle is viewed slightly less favourably than her husband, with 22 percent holding a positive view of her compared to 29 percent for Harry.

But the majority of the public view both royals unfavourably (65 percent for Meghan and 61 percent for Harry).