Former South African President Nelson Mandela died Thursday at the age of 95 after a long illness.
London's Daily Express newspaper said the prince was informed of Mandela's death while the film was screened at the Odeon Leicester Square.
"We were just reminded what an extraordinary and inspiring man Nelson Mandela was. My thoughts and prayers are with him and his family," Prince William said as he and Kate were leaving after the screening. "It's very sad."
The Express said two minutes of silence was observed at the end of the film in honor of the international human rights icon.
Yahoo! Movies reported Zindzi, Mandela's 55-year-old daughter, was overcome with emotion at the screening and departed without speaking to the press.