ONE Direction reunited at 'The X Factor' on Saturday, to support Louis Tomlinson.
Harry Styles, Niall Horan and Liam Payne were all backstage with Louis at the show, where he performed his new single 'Just Hold On' for the first time, in tribute to his late mother Johannah Deakin, who passed away earlier this week after a secret battle with leukaemia.
The group have been on hiatus for almost a year but the trio dropped everything to be with Louis after he decided to go ahead with the performance, which had been planned for some time and which his mother had been looking forward to.
A source told MailOnline: "Harry, Niall and Liam all came down to X factor to support Louis. They all were backstage with him supporting him. It was a lovely moment - and shows the unity of 1D. First time all back together in a year.
"It was a lovely touching moment backstage and they all came to support Louis during a horrible time. Niall even flew back from New York."
However, Louis admitted getting up on stage just days after Johannah's death, was "harder than I ever imagined".
He tweeted: "That was harder than I ever imagined. I want to thank everyone around me and all of the amazing fans out there that made that so special!
"Feeling so much love around me and my family. Mum would have been so f**king proud ( sorry for swearing mum ) love you ! (sic)."
He also praised his collaborator Steve Aoki as a "rock", saying: "Also @steveaoki , you have been such a rock and inspiration throughout this ! Pure talent and a real gent ! (sic)."
However, Steve insisted Louis was the rock and called him his inspiration.
He tweeted: "U were the rock my brother. U are my inspiration. U have the biggest f**king heart and I'm so proud of u. Blew us all away for her (sic)."
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 24-year-old singer bravely took to the stage to perform the track, which features the poignant lyrics: "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."
The upbeat song - which ended with the four judges, Simon, Sharon Osbourne, Louis Walsh and Nicole Scherzinger, and the 12,000 strong crowd at Wembley Arena giving Louis an extended standing ovation - also features the lyrics: "If it all goes wrong, darling just hold on / The sun goes down and it comes back up / The world, it turns no matter what / If it all goes wrong, darling just hold on."