This will be the first time a senior British royal has given evidence in court in over 130 years.
Harry is suing the newspaper group along with over 100 other celebrities and high-profile figures.
The trial is expected to attract worldwide attention, with the royal family seeking to avoid court cases due to their lack of control in the situation.
Former editor Piers Morgan is among those who knew about the alleged hacking, and has denied any involvement in unlawful behavior.
The court has already heard that senior editors and executives at the newspaper group knew about hacking and concealed any wrongdoing.
Prince Harry will appear at the High Court in London for the second time this year on Wednesday.
He will join singer Elton John and others in a lawsuit against the publisher of the Daily and Sunday Mail tabloids over alleged phone hacking.
The palace has not commented on the matter.
LONDON DAILY ARCHIVE
Prince Harry to Testify in Landmark Trial Against Newspaper Group for Alleged Phone Hacking
Prince Harry will testify in court as part of a lawsuit against a newspaper group for alleged unlawful behavior, including phone hacking.
03 June 2023 · 21:06 UTC
