Back in 2015, Red Bull was running Renault engines in F1 and whilst Mercedes was dominant at the front of the field, the French manufacturer had failed to get to grips with the sport's new turbo-hybrid V6 power unit regulations - introduced in 2014.
According to rumours at the time, Red Bull was knocking on Mercedes' door with a view to taking on a customer supply.
Mercedes Team Principal Toto Wolff claimed at the time that a deal was never on the table, but then Non-Executive Chairman Niki Lauda made noises on the contrary.
According to the Austrian, a deal was very much in the offing and would have been completed had Red Bull continued its own pursuit.
Speaking to Sky Sports about the rumours, Lauda - who passed away in 2019 - revealed: "Christian Horner and Helmut Marko sent us a letter to express interest in our engines. I replied 'fine, but let's discuss things with Dietrich Mateschitz first.
"Mateschitz namely, for whatever reason, had never been a fan of Mercedes. There was something going on in the past that I didn't know about.
"So when I asked Mateschitz if he was interested he said 'yes, but, but, but, but...'"
"There was no follow-up to that 'but, but, but...' We had to make a decision then. Who got our engines? We also didn't know if Lotus would stay [as a Mercedes customer], so then we decided to give our engines to Manor."
Since then, Red Bull remained with Renault before switching to Honda, gaining great success with the Japanese manufacturer and going toe to toe with the Silver Arrows.