Troy Austin split from the singer's mother, Johanna, when Louis was aged two and the pair lost touch over the years.
Austin reveals he and his daughter Georgia, the star's half-sister, attended a One Direction concert in the U.K. this month (Mar13), and he is eager to get back in contact with his son, who he last saw in 2010 when the star auditioned for Britain's The X Factor, the show which launched him to fame with the band.
He tells the U.K.'s Sunday Mirror, "Seeing Louis on that stage was amazing. He's in the biggest band in the world and I'm the proudest dad in the world. I just hope he knows it.
"It was a shame we couldn't see Louis and tell him how brilliant he was. But I know he and the rest of the lads are really busy. Georgia was gutted - she's his half-sister after all. I haven't been there for most of his life, so I understand I'm not one of his main priorities.
"He knows we were in the crowd and now I want to tell him what it meant to me to see him up there. I cried buckets...
"Me and his mum splitting up when he was so young wasn't anyone's fault... I know it was hard on him. Seeing what he's done with his life makes me so happy. I know people will think I'm only interested in being part of his life again because he's rich and famous. But it's not about that. I'm his dad. We're flesh and blood and nothing can change that. I'm so proud of him I could burst.
"Of course, I would love to see him again and have a proper relationship with him. What dad wouldn't? But it's up to him. I want him to know I think he's fantastic - and that Georgia is his biggest fan."