Thousands of Dion devotees flooded the park to watch Celine as she delivered her most famous hits, and Smith took to Instagram to rave about the show.
Sharing a video of his thrilled reaction to Celine's performance of "It's All Coming Back To Me Now", he wrote the caption: "CELINE DION JUST CHANGED MY LIFE."
British royals Princesses Beatrice and Eugenie were also spotted in the crowd at the concert
The "My Heart Will Go On" singer, who kicked off the show in an electric blue jumpsuit, had a special message to her fans as she became the first of the five 2019 British Summer Time show headliners, telling them, "We are so excited to be with you this evening in beautiful Hyde Park and you are looking incredible. You know, we've always loved coming to the U.K. and doing shows here, but this is extra, extra special for us tonight."
Celine played hits like "Think Twice", "The Power of Love", "My Heart Will Go On", and "All By Myself" and covers of Prince's "Purple Rain" and Ike & Tina Turner's "River Deep, Mountain High", before closing her set with a cover of John Lennon's "Imagine" and calling for "peace and harmony".
"If I may, I would love to leave with this message of peace and harmony in the best way that I can," she said.