The future monarch, 11, joined William and his mother the Princess of Wales , along with the King and Queen and other members of the Royal Family at the Palace tea party.
Zelensky said Ukraine would not be "playing games to create a pleasant atmosphere" on May 9, when some foreign leaders are due in Moscow for WWII commemorations.
The chilling discovery was made in the city of Lodz by researchers from the country's Institute of National Remembrance which is tasked with investigating WWII crimes.