Zayn Malik's mother burst into tears when he bought her a mansion costing hundreds of thousands of pounds.The One Direction singer splashed out on the luxury home in his hometown of Bradford, West Yorkshire, for his mum Tricia Brannan, who describes her dream home as "lovely" before getting teary about her son's kind gesture. Seen in the latest trailer for the boy band's forthcoming 3D documentary film, 'This Is Us', an emotional Tricia is seen picking up the keys and visiting the property with two of the 20-year-old hunk's three sisters. She then calls Zayn and says: "Hello sunshine. I know that you always used to say, 'I'll get you a house one day when I'm older.' But thank you for what you've done for us. I'm so proud of you."While holding back the tears, Zayn replies: "Well, get off the phone then before I start crying."Despite amassing fortunes of around £5 million each since shooting to fame on talent show 'The X Factor' in 2010, Zayn insists the 'Little Things' hitmakers - who are also made up of Niall Horan, Harry Styles, Louis Tomlinson and Liam Payne - have remained grounded. He added: "We just come from normal working-class families."Last year, it was revealed Tricia had several obscure objects in her family home emblazoned with Zayn's picture on, including a huge, clock. A source said at the time: "Zayn's mum has an enormous clock with his face as the background on their mantelpiece."He's a hero in that house and there are Zayn tea towels and pictures of him all over the place."