The Duke of Kent represented King Charles at Wednesday's VE Day Concert, according to a statement from Buckingham Palace.
The late Queen Elizabeth II's first cousin is Prince Edward, the 89-year-old Duke of Kent.
His wife, Katharine, Duchess of Kent, is the oldest living member of the British royal family, at 92.
According to the release, the Parliament Choir performed the concert in Westminster Hall.
It stated: "The 100-strong Parliament choir, supported by Sinfonia Smith Square Orchestra, performed classical music from countries around Europe to celebrate 80 years of peace."
The Duke of Kent recently attended a ceremony at Windsor Castle, where he was accompanied by Chief Scout Dwayne Fields.
When the palace posted photos from the ceremony, royal family followers praised the 89-year-old for his commitment to royal duties.
"The Duke of Kent is the epitome of duty and loyalty," a devotee said.
A other individual commented, "HRH The Duke of Kent is a true stalwart of the royal family."