Niall Horan has paid tribute to his former One Direction bandmate Liam Payne, saying he is "absolutely devastated" by his death.
The 31-year-old pop star suffered "extremely serious injuries" after landing in the courtyard of the CasaSur Hotel in the Argentinian capital Buenos Aires, police said.
Payne had flown to Buenos Aires to attend the Horan's concert at the Movistar Arena earlier this month.
Paying tribute to Payne, Horan shared a photo of the pair as teenagers at the start of their One Direction journey, with his bandmate on his back and both smiling for the camera.
In a statement shared on Instagram, he wrote: "I feel so fortunate that I got to see him recently. I sadly didn't know that after saying goodbye and hugging him that evening, I would be saying goodbye forever. It's heartbreaking."
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He described his former bandmate as having an "energy for life and a passion for work that was infectious".
"He was the brightest in every room and always made everyone feel happy and secure," he said.
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He went on: "All the laughs we had over the years, sometimes about the simplest of things, keep coming to mind through the sadness.
"We got to live out our wildest dreams together and I will cherish every moment we had forever. The bond and friendship we had doesn't happen often in a lifetime."
He said news of the death of his "amazing friend" just didn't "feel real".
He signed off his post, "Thank you for everything Payno, Love you brother, Nialler".
Former One Direction members Harry Styles, Louis Tomlinson, Zayn Malik and Niall Horan put out a statement saying they were "completely devastated" following Payne's death.
Read more:
Liam Payne dies - what we know so far
Payne posts on Snapchat hours before death
Fans flocked to the hotel after news of Payne's death broke, setting up vigils, singing and lighting candles.
In the UK, fans are planning a memorial in Hyde Park in London on Sunday afternoon.
The band was formed on The X Factor in 2010, with Payne featuring alongside Horan, Zayn Malik, Louis Tomlinson, and Harry Styles. They were mentored by Simon Cowell, who had also created the show.
The group finished third before signing with Cowell's "Syco" record label and going on to become one of the best-selling boy bands of all time.
Payne leaves behind his 7-year-old son Bear who he shared with Girls Aloud star Cheryl, his parents Karen and Geoff, and elder sisters Nicola and Ruth.