Red Bull Formula 1 team principal Christian Horner has revealed what sparked the ‘Multi 21’ controversy between former drivers Sebastian Vettel and Mark Webber.

The pair endured a fractious relationship during their five-year spell as teammates at the Milton Keynes-based squad, with tensions reaching boiling point at the 2013 Malaysian Grand Prix.

With Webber leading a comfortable Red Bull 1-2 in Sepang, Vettel defied instructions from the Red Bull pit wall to hold position and overtook his teammate to win the race, prompting an angry response from the Australian.

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But Horner explained Vettel’s decision to ignore team orders had been in response to an incident that occurred just two races earlier at the season-ending 2012 Brazilian Grand Prix. With Vettel in a direct title battle with Ferrari’s Fernando Alonso, Webber squeezed the German up against the wall on the run to Turn 1 at the start, causing Vettel to lose momentum, before he ultimately got caught up in an incident a few corners later and dropped to the rear of the field.

“It was very difficult for Mark to accept at the time that, and I think if he looked back at it now with perspective and honesty, Sebastian was just quicker,” Horner told the official F1 podcast. “So therefore Mark would use whatever tool he could to try and get under his skin.

“As a team, we were just trying to play a straight bat, but every now and again, you’d get a missile coming in and the situation got tougher and tougher.

“It probably culminated at the end of 2012 when Sebastian was fighting Alonso for the championship and Mark squeezed him up against the pit wall at the start of the race in Brazil, in the championship decider, which ultimately resulted in him getting turned round by Bruno Senna. Sebastian was hugely angry about that.

“There was a hangover of that that led into Malaysia, literally two races later, split by four or five months. You had a situation where you have Mark in the car ahead, Sebastian on new tyres in the car behind. The tyres were pretty fragile, we’re telling them hold position and Sebastian thought ‘F*** you’.”

When asked if he believed Vettel’s actions had acted as payback, Horner replied: “100%. [Vettel] told [Webber] that after the race or when they sat down in China. That was probably as tense as it could get.”

Horner described how the incident led to an unexpected conversation with The Queen over lunch during a visit to Buckingham Palace.

“I had been invited to a lunch hosted by The Queen and the Duke of Edinburgh, which I expected there to be about 200 people at. There turned out not be 10 of us there. This was at Buckingham Palace. It was just after the 'Multi 21' scenario,” he said.

“I had this bizarre situation of having to deal with the drivers and then go to lunch with The Queen and Prince Philip and explain to her what ‘Multi 21’ was and why our Australian driver was particularly grumpy with our German driver. I had that conversation over lunch with The Queen and she seemed to show great interest in it.”