BACK TOGETHER: One Direction reunite backstage at the X Factor to support Louis Tomlinson after mum’s death
The boys joined Louis in his dressing room to support him after the death of his mum Johannah at the age of 43
The chart-topping bandmates have not been in the same room together since last December after going on a long-term hiatus.
But an X Factor source revealed: “Harry, Niall and Liam all wanted to be there to support Louis tonight for what was undoubtedly one of the most difficult moments of his life.
“It was an incredible and special thing for them to get back together as a four and be like brothers again.
“Niall flew in overnight from New York so he could be there and Liam came from Los Angeles. It was that important they were together.
“They were all in Louis’s dressing room together and it was obviously an incredible emotional night.”
The world’s biggest band were discovered on X Factor in 2010 and signed to Simon Cowell’s record label Syco.
But the last year has seen them go their separate way, with all four members launching their own solo careers.
Former member Zayn Malik was not backstage at X Factor for the reunion, but tweeted his support to Louis after learning of Johanna’s death.
Louis, 24, performed his debut single Just Hold On with DJ Steve Aoki as a tribute to Johannah, who died on Wednesday after a long secret battle with leukaemia.
Speaking after the performance, Simon Cowell told a tearful Louis: “I have to say something to you. I’ve known you for six years, what you’ve just done - the bravery.
"I respect you as an artist and I respect you as a person. Your mum was so proud of you Louis and she was so looking forward to this performance. She’s watching over you now and you’ve done her so proud.”
The poignant lyrics to the song include: “What do you do when a chapter ends / Do you close the book and never read it again / Where do you go when your story’s done / You can be who you were or who you’ll become.”
Louis tweeted on Saturday afternoon: “All the support has been incredible! Let’s do this together tonight.”