Prince George and Princess Charlotte Join Royal Family for Platinum Jubilee Concert at the Palace

The starry concert at the palace celebrating the Queen's 70-year reign features Diana Ross and Alicia Keys

The 96-year-old monarch opened the doors of Buckingham Palace to 22,000 guests on Saturday

for a star-studded "Platinum Party" celebrating the U.K. and Commonwealth's contributions to fashion

sports, the environment and music during her record-breaking 70-year reign.

The Queen herself did not attend the concert due to her ongoing "mobility issues."

PEOPLE has confirmed that she will be watching the show on TV at home in Windsor Castle

but her absence didn't dampen the celebration.

Meghan Markle and Prince Harry also did not attend the festivities.

The couple is spending the day privately as a family to celebrate their daughter Lilibet's first birthday.