Former One Direction member Niall Horan was one of the special guests in Taylor Swift's Reputation concert in London this week.

Niall Horan Performs 'Slow Hands' With Taylor Swift

The Irish singer joined Swift onstage to perform his solo hit single "Slow Hands" at the Wembley Stadium on Friday, June 22.

The show marks the first time that the 28-year-old pop superstar performed at the Wembley Stadium. A second show is scheduled at the same arena on Saturday, June 23, reported The Independent.

Since the Red tour in 2012, it has become a tradition for Swift to invite her famous friends to make appearances at her concerts. In the past few weeks, she has welcomed Shawn Mendes, Troye Sivan, and her celebrity best friend Selena Gomez at different dates and venues of the ongoing Reputation stadium tour across North America. Camila Cabello and Charli XCX also grace the stage as supporting acts.

This is the first time that Swift invited Horan during her concert series.

On Instagram, the "Delicate" singer announced the former One Direction member's appearance in her London concert by posting photos of the two of them chilling inside Wembley Stadium.

The fans, however, were not suspecting the surprise. Footage taken from the show revealed that the audience totally freaked out when Horan appeared onstage.

The 24-year-old released his first solo album, Flicker, in October 2017. "Slow Hands," one of the lead singles of the LP, peaked at the 11th spot of the Billboard Hot 100 and on No. 7 of the Official U.K. Singles Chart. Horan also released "This Town" and "Too Much To Ask."

Taylor Swift Makes History In Ireland

After Saturday night's show, Swift will be heading back to the United States to continue the North American leg of the Reputation tour. However, before leaving Europe, the chart-topping artist managed to mark her name into history.

The "Bad Blood" singer just became the first woman to sell out two nights in a row at the Croke Park in Ireland, reported The Irish Sun.

Croke Park, located in Dublin, has a capacity of around 82,300 people. It is also the largest sporting arena in Ireland and the third largest stadium in Europe.

Beyonce, Celine Dion, and Tina Turner have previously performed at the venue to sold out shows, but Swift is the only female to fill the stadium for two consecutive nights.

The "Look What You Made Me Do" singer will next perform at the Papa John's Cardinal Stadium in Louisville, Kentucky on June 30.