By Niamh Spence Singer Ariana Grande made a surprise appearance at the Met Gala as she took to the stage to perform some of her greatest hits. The 30-year-old performed for attendees of the Met Gala as she gave a whistle stop tour of her greatest hits including singing Disney’s “Once Upon a Dream,” before then singing five of her own songs “Into You,” “Seven Rings,” “The Boy Is Mine,” “We Can’t Be Friends,” and “Yes, And”, before she finished off with a cover of “When You Believe” with her Wickedco-star Cynthia Erivo. Ariana initially wore an elegant white Loewe dress with a pleated skirt on t…