The music mogul joined Harry Styles, Zayn Malik, Niall Horan, Louis Tomlinson and Liam Payne on the red carpet in London's Leicester Square on Tuesday night (20 August).
Simon's kept a relatively low profile following those claims that New York socialite Lauren Silverman is pregnant with his first child, but it was only appropriate he was at the premiere given his role in creating One Direction.
The 53-year-old was the head judge on X Factor's seventh season when the five boys auditioned as solo artists. They didn't progress as soloists, instead being put together as 1D and, as they say, the rest is history!
Simon looked happy on the red carpet and even managed to joke about the love child reports, telling the crowd: "This is like a dream come true... I feel like a father!"
His long-time friend and former girlfriend Sinitta was also at the screening, as was his most recent ex-girlfriend, Mezhgan Hussainy.
Thousands of fans packed into Leicester Square - some camping for as many as three days - in the hopes of catching a glimpse of their idol. Or, even better, getting a coveted autograph or picture.
On arriving, Niall said: "We just want to say a massive thank you. We can't believe we're here in Leicester Square with all you crazy people. We love you all. Two years ago we were on the X Factor and here at the same place for the Harry Potter premiere.
"We just want you to know when you go and watch this movie and look around here tonight at these big screens and posters you have done all of this. Thank you so much for everything over the last three years. We love you so much."
This Is Us, directed by Morgan Spurlock, is a feature-length documentary that will give fans an insight into the band's daily lives, featuring exclusive performances, behind-the-scenes footage and interviews with friends and families.
The movie opens on Thursday.
Watch a trailer for This Is Us below: