Niall Horan, Liam Payne and Louis Tomlinson came suited and booted at the Great Gatsby Charity Ball in support of Trekstock in London (16 April), however, they were without fourth band member Harry Styles.
Looking grown-up in suits, the boys had huge smiles on their faces as they joked around while posing for photos.
While Niall looked smart in a white suit jacket and black trousers, Louis opted for all-black, while Liam - who arrived with his girlfriend Sophia Smith - wore a blue suit.
Sophie Epstone, founder of young adults cancer charity Trekstock, commented: "A massive thank you to Liam Payne, an ambassador of Trekstock and an unwavering champion of our cause, whom without doubt ensures we maintain our authentic voice."
Last month, Zayn announced his decision to quit the band, just a week after pulling out of the world tour due to stress.
Zayn said in a statement: "I am leaving because I want to be a normal 22-year-old who is able to relax and have some private time out of the spotlight."
Despite Zayn's departure, 1D said they would continue as a band, saying they "totally respect" Zayn's decision to quit. As a four-piece, One Direction are now focusing on their world tour and fifth studio album.
Earlier this week, Niall, Liam, Louis and Harry posed in their first official photo as a four-piece to mark their new chapter in the band.
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