Prince Harry and Meghan Markle's Archewell Foundation received a large part of the donations from a single donor in 2021.
Omid Scobie, a royal correspondent and co-author of an authorized biography of Meghan and Harry, said the total donations in the organisation's first year of operation amounted $13million.
The couple's non-profit organisation shared its impact report at the end of January.
The author of "Finding Freedom" said the foundation distributed $3m in grants across a number of areas Meghan and Harry have been focusing on in recent years - including vaccine equity, refugee resettlement, relief centres and the creation of a "better online world".
Citing an investigation, express.co.uk reported that in the first full year of operation, Archewell had one particularly generous donor to thank for the money raised, as this unidentified wealthy person alone donated $10m.
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