Olivia Dean headlined the third night of Lollapalooza 2026 in Chicago's Grant Park on Saturday, bringing out Sam Fender as a surprise guest to perform their duet "Rein Me In" — the song that, the Friday before, set a new U.K. record for the longest run at Number One on the singles chart.

The moment nearly did not happen on schedule. Overnight rain flooded Chicago and continued through Saturday, pooling across Grant Park and forcing Lollapalooza to push back its doors by roughly three hours for cleanup. The festival opened at 3 p.m. with muddy but navigable grounds, according to Rolling Stone. Some performances were cancelled outright and others were truncated to fit the compressed schedule.

Dean's ascent to the T-Mobile stage headlining slot has been swift. She last played Lollapalooza in 2024 on a smaller daytime stage, and her first headlining show in Chicago drew about 1,500 people. In February 2026 she won the Grammy for Best New Artist. Her sophomore album, The Art of Loving, was the first Official Number 1 album of 2026 in the U.K. and went on to become the biggest U.K. album of the first half of the year, according to midyear chart data published by Hits Daily Double on 17 July.

The numbers around "Rein Me In" are what made Fender's appearance land with particular force. The duet spent 19 weeks atop the U.K. singles chart, breaking a record held for more than 70 years by Frankie Laine's "I Believe," which spent 18 weeks at Number One in 1953. "Rein Me In" was also the biggest U.K. single of the first half of 2026, per the same midyear chart data. On 3 October 2025, Dean achieved a rare chart double — reaching Number One on both the U.K. albums and singles charts simultaneously, as confirmed by Billboard.

Her Lollapalooza set drew from both of her albums: the debut Messy (including "Dive") and The Art of Loving. The full setlist, per Yahoo UK, ran through "Nice to Each Other," "Lady Lady," "So Easy (to Fall in Love)," "Close Up," "Let Alone the One You Love," "Messy," "Carmen," and "Echo," before Fender joined her onstage for "Rein Me In."

Earlier in the day, 20-year-old Sienna Spiro performed on the Airbnb stage, drawing from her debut album Visitor. Her set included "Pure," "He's Not My Baby, I'm His," "Great Expectation," and closed with "Die on This Hill."

For Dean, the evening capped a year in which the gap between a daytime stage and a headlining slot closed in a single festival cycle. For the crowd wading through Grant Park's mud, the three-hour wait bought them a headline set and a surprise guest appearance tied to a piece of chart history.