Niall Horan has said he will "cherish every moment" he had with Liam Payne "forever" following the death of his One Direction bandmate.
In a post on Instagram, the Mullingar man 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."
Alongside a picture of himself with Payne from One Direction's early years, he added: "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.
"My love and condolences go out to Geoff, Karen, Ruth, Nicola and of course his son Bear. Thank you for everything, Payno. Love you brother."
Earlier, Payne's One Direction bandmates said they are "completely devastated" and will miss the singer "terribly".
A statement signed by Harry Styles, Zayn Malik, Louis Tomlinson and Horan said: "We're completely devastated by the news of Liam's passing.
"In time, and when everyone is able to, there will be more to say.
"But for now, we will take some time to grieve and process the loss of our brother, who we loved dearly.
"The memories we shared with him will be treasured forever.
"For now, our thoughts are with his family, his friends, and the fans who loved him alongside us.
"We will miss him terribly. We love you Liam."
In an Instagram post, former One Direction star Tomlinson said he has "lost a brother".
"I am beyond devastated to be writing this but yesterday I lost a brother. Liam was somebody I looked up to everyday, such a positive, funny, and kind soul.
"I first met Liam when he was 16 and I was 18, I was instantly amazed by his voice but more importantly as time went on I got a chance to see the kind brother I'd longed all my life for.
"Liam was an incredible song writer with a great sense of melody, we often spoke of getting back in the studio together to try and recreate the writing chemistry we had built up in the band.
"And for the record, Liam was in my opinion the most vital part of One Direction. His experience from a young age, his perfect pitch, his stage presence, his gift for writing. The list goes on. Thank you for shaping us Liam."
He added: "A message to you Liam if you're listening,
"I feel beyond lucky to have had you in my life but I'm really struggling with the idea of saying goodbye. I'm so grateful that we got even closer since the band, speaking on the phone for hours, reminiscing about all the thousands of amazing memories we had together is a luxury I thought I'd have with you for life. I would have loved to share the stage with you again but it wasn't to be.
"I want you to know that if Bear ever needs me I will be the Uncle he needs in his life and tell him stories of how amazing his dad was.
"I wish I got [the] chance to say goodbye and tell you one more time how much I loved you.
"Payno, my boy, one of my best friends, my brother, I love you mate. Sleep well X."
Malik also mourned the loss of his former One Direction bandmate in an emotional tribute on Instagram. Alongside his touching post, he shared a throwback photo of the pair sleeping in a car.
Malik said he "never got to thank" Payne for supporting him through some of the "most difficult" times in his life.
"Liam, I have found myself talking out loud to you hoping you can hear me, I can't help but think selfishly that there were so many more conversations for us to have in our lives. I never got to thank you for supporting me through some of the most difficult times in my life. When I was missing home as a 17 yr old kid you would always be there with a positive outlook and reassuring smile and let me know you were my friend and I was loved.
"Even though you were younger than me you were always more sensible than me, you were headstrong, opinionated and gave no f***s about telling people they were wrong. Even though we butted heads because of this a few times, I always secretly respected you for it.
"When it came to the music Liam, you were the most qualified in every sense. I knew nothing in comparison, I was a novice child with no experience and you were already a professional. I was always happy to know, no matter what happened on stage we could always rely on you to know which way to steer the ship next."
He added: "I lost a brother when you left us and can't explain to you what I'd give to just give you a hug one last time and say goodbye to you properly and tell you that I loved and respected you dearly. I will cherish all the memories I have with you in my heart forever.
"There is no words that justify or explain how I feel right now other than beyond devastated. I hope that wherever you are right now you are good and are at peace and you know how loved you are. Love you bro."
Styles also joined his former bandmates in paying tribute to their late friend, saying "he had an energy for life".
"His greatest joy was making other people happy, and it was an honour to be alongside him as he did it," he said.
"Liam lived wide open, with his heart on his sleeve, he had an energy for life that was infection [sic]. He was warm, supporting, and incredibly loving. The years we spent together will forever remain among the most cherished years of my life. I will miss him always, my lovely friend."
Styles extended his thoughts to Payne's family as well as "all those around the world who knew and loved him, as I did".
Liam Payne's family said they are "heartbroken" by the singer's death and said he will "forever live in our hearts".
The singer died after falling from the third-floor balcony of a hotel in Argentina.
Local police said the 31-year-old fell into the courtyard of the Casa Sur Hotel in the Palermo neighbourhood of Buenos Aires before medics confirmed his death.
A statement from his family, issued via a spokeswoman to the PA news agency said: "We are heartbroken.
"Liam will forever live in our hearts and we’ll remember him for his kind, funny and brave soul.
"We are supporting each other the best we can as a family and ask for privacy and space at this awful time."
Shocked fans gathered outside the hotel after police cordoned off the area on Wednesday night. Forensic investigators in white protective suits and blue gloves were seen entering and leaving.
Fans were photographed lighting candles and leaving flowers at the side of the road in an impromptu vigil as they paid tribute to the music star.
Police in Argentina are now investigating the circumstances around Payne's death. A preliminary autopsy showed the 31-year-old singer suffered "internal and external bleeding" and "died from the fall" a police source told AFP.
Payne formed boy band One Direction in 2010, alongside Zayn Malik, Louis Tomlinson, Niall Horan and Harry Styles, after they individually auditioned for The X Factor.
After becoming one of the biggest pop groups in the world, with five albums and four world tours, they went on indefinite hiatus in 2016.
Read more:
'He just loved to sing' - tributes paid to Liam Payne
Liam Payne: Teenager thrust into global boyband mania who dealt with early fame
In Pictures: Liam Payne from X Factor to stardom
