Meghan Markle and Prince Harry's former Sussex Royal charity did not break the law in transferring funds to the Duke of Sussex's Travalyst organisation.
The charity was investigated after pressure group Republic reported Sussex Royal to the Charity Commission for alleged "inappropriate use of charitable funds, conflicts of interest and lack of independence".
The Duke and Duchess of Sussex founded Sussex Royal as they broke away from the Royal Foundation, which they once ran with Prince William and Kate Middleton.
But after launching an investigation in July 2020, the Commission found that MWX - which was formerly Sussex Royal: The Foundation - did not act outside charity law.
The investigation revealed that the transfer of funds to not-for-profit sustainable travel organisation Travalyst was lawful and in line with the governing document of the Royal Foundation and allowed under charity law.
The Commission also found that Travalyst could receive charitable funds for the promotion of sustainable travel only, which is a charitable activity in law.
There was no evidence to suggest that any conflicts of interest between MWX and Travalyst were managed inappropriately, the Commission found.
Republic - which campaigns to see the monarchy abolished and the Queen replaced with an elected, democratic head of state - has issued a lengthy apology on its website.
It said that it "falsely claimed" the transfer of funds was improper and likely to be unlawful and that it failed to contact the Royal Foundation or Sussex Royal before going to the Commission and the media.
The pressure group said: "If we had contacted the organisations directly, we accept we would have realised quickly that there was nothing improper in their operations.
"The Charity Commission has now concluded its review and found that all activities of the charities were lawful and proper.

"We apologise unreservedly to the charities and personally to the Duke of Sussex for our actions and the public damage that has been caused as a result of widely publicised untrue claims."
Harry and Meghan shut down Sussex Royal in July after their move the US.
Shortly after, they announced plans for their new not-for-profit organisation, Archewell.
A spokesperson for Harry and Meghan said: "We are pleased that the Charity Commission has confirmed what we knew from the start: that MWX Foundation, formerly Sussex Royal, complied fully with UK charity law in its handling and transferring of funds and grants.
"Today's update provides complete closure to this review and ultimately underscores both the legitimacy of the former charity and the baselessness of the claims against it."