The famous duo were among the special guests at the The Prince's Trust & Samsung Celebrate Success Awards, which honour young people who overcome adversity with the help of the first-in-line to the throne's charity.
Prince Charles chatted with Mirren, who famously played his mother Queen Elizabeth Ii in The Queen, and joked to the star-studded crowd about the Oscar winner's current turn as the monarch in West End show The Audience.
In his speech to the crowd, he said, "I have a feeling that Dame Helen Mirren should really be putting on a familiar wig in some West End theatre now."
Moved to tears by the award winners' stories, Mirren added, "All the young people here today are truly inspirational. Their remarkable stories have blown me away."
Other guests included The Prince's Trust ambassadors Mark Ronson, actor Idris Elba, and Lewis, who was on hand to present an award to Afsana Benozir, a former victim of child abuse who is now heading to medical school.
The Homeland star said, "Afsana's story is truly remarkable. I'm honoured to have met her."