The 57-year-old music mogul signed the chart-topping boyband - which features Niall Horan, Liam Payne, Harry Styles, Louis Tomlinson, and previously, Zayn Malik - to his label in 2011, and Simon still feels an incredibly strong bond with the group.
Speaking about Louis' debut solo single 'Back to You', Simon shared: ''Louis and I, you know, we've got this very close bond. When we heard about this current record, I remember calling him and going, 'Louis, this record is special' - and I could not be happier.
''Actually, with all the boys, if I'm being honest with you. They've worked for this. But yeah, you do feel a little bit like a proud dad when you see all five of them doing well now.''
Simon's relationship with Louis was solidified after he gave the singer a much-needed pep talk during his One Direction days.
The TV star said his straight-talking approach proved to be a turning point in their dynamic.
Recalling the incident, Simon told Billboard: ''When somebody goes a little bit crazy, my way of dealing with things is to deal with it straight away, face-to-face.
''I sat him down and went, 'Look, we've all been there, I've been there. You're in a fantastic place right now.' ... And then we laughed it off, he sent me a very nice text afterwards and from that moment we had this incredible bond.''
Louis has also admitted the dressing down from Simon marked an important milestone in their relationship, revealing it brought them closer together.
The singer recently confessed: ''I do really feel like he's got my back, you know.
''I've done quite a lot with him even outside of One Direction. And actually, I think it was vital for me as an individual and also our relationship.''
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