The so-called Paradise Papers have revealed Britain's Prince Charles allegedly campaigned to alter climate-change agreements without disclosing the offshore financial interests of his estate.
The leaked documents showed his estate, the Duchy of Cornwall, secretly bought shares worth US$113,500 (€97,925) in a firm in Bermuda in 2007 that could benefit from changes in rules, according to the BBC's Panorama.
It claimed Prince Charles was a friend of one of the directors of forest management company, Sustainable Forestry Management Ltd.
But the Duchy of Cornwall said Prince Charles had no direct involvement in any of its investments.
A spokesman for Clarence House said he had "never chosen to speak out on a topic simply because of a company The Duchy may have invested in".
He added: "In the case of climate change his views are well known, indeed he has been warning of the threat of global warming to our environment for over 30 years.
"Carbon markets are just one example that the Prince has championed since the 1990s and which he continues to promote today."
A Duchy of Cornwall spokesman said the estate had a "responsible investment policy" and that its accounts were "independently audited and presented to parliament every year".
He added: "These investments do not derive any tax advantage whatsoever based on their location or any other aspect of their structure and there is no loss of revenue to HMRC as a result."
The revelation comes after the private estate of Britain's Queen Elizabeth II was accused of investing millions of pounds in offshore tax havens.
Bono, tech giant Apple and Formula One champion Lewis Hamilton have also been named among those allegedly avoiding tax.
The Taoiseach Leo Varadkar has insisted the Revenue Commissioners will pursue anyone shown to have avoided Irish tax.