Brad Pitt and Angelina Jolie have openly admitted they fell in love on the set of their 2005 movie Mr & Mrs Smith - while Brad was still married to Jennifer Aniston.
But they were so sneaky at the time that they even managed to hide their secret feelings for each other from their bodyguard.
A British man who was appointed as their close protection officer on the set of the film says he had no idea that there was something going on between them.
The bodyguard, who we are keeping anonymous, exclusively told Mirror Online about his time behind the scenes on the movie.
He told us: "I was the main detail leader for Mr & Mrs Smith's afterparty, which was at 4 o'clock in the morning.
"I got called up at 4 in the morning to go to this speed zone, where they do drag racing and bumper cars and things like that - it was a big field.
"Brad was there, Angelina was there, and the whole crew."
He added: "We had to make sure there was no paparazzi around, it was really secretive, a massive secret, and everyone was reporting that those two were together.
"I even had my mum telling me she'd read in the papers that they were together and I was saying, 'Mum, there's no way, I'm with them every day, there's no way anything's going on'.
"And low and behold, was I wrong!
"How did the media know about it and I didn't? I was there on set."
Brad, 56, was married to Friends star Jennifer when he began working on the movie in 2004.
They had tied the knot in 2000 and later divorced in 2005.
Brad and Angelina, 44, denied rumours of a romance and insisted they were just close friends.
Angelina, who was fresh off her divorce from Billy Bob Thornton when filming started, said at the time: "We spent a lot of time contemplating and thinking and talking about what we both wanted in life and realized that we wanted very, very similar things."
She later said that the defining moment in their relationship was when her son Maddox, who she had adopted in 2002, started calling Brad "dad".
They went public with their romance after Brad's divorce was finalised in 2005, but vowed not to get married until gay couples were afforded the same right.
The couple went on to adopt two more children, Zahara and Pax and have three biological children, Shiloh and twins Knox and Vivienne.
In 2008, Angelina raised eyebrows when she confessed she and Brad had fallen in love on the set of their movie.
She told the New York Times that she looked forward to the day her kids were old enough to watch Mr & Mrs Smith, saying: "Not a lot of people get to see a movie where their parents fell in love."
Later that same year, Brad confirmed it when he described the flick as his favourite film.
When asked why, he told Rolling Stone: "Because you know... six kids. Because I fell in love."
Brad and Angelina divorced in 2016.
Since then, there have been lots of rumours that Brad has rekindled his romance with Jennifer, 51.
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