Red Bull motorsport boss Helmut Marko has revealed how a faltering Daniil Kvyat at Red Bull and tensions between the Verstappen and Sainz camps led to a driver switch in early 2016.
Just four races into the 2016 season, Marko opted to demote Kvyat to Toro Rosso and to replace the Russian with Max Verstappen at Red Bull Racing.
Kvyat had come under fire at his home race at Sochi for a run-in with Ferrari's Sebastian Vettel, and that incident was thought to have decided Red Bull to undertake a driver swap.
But in a recent interview with Germany's Auto Motor und Sport, Marko revealed the real reasons for the permutations that led to Verstappen winning his maiden Grand Prix on his first race with Red Bull Racing.
"Kvyat was faster than Ricciardo in his first year at Red Bull," explained the Austrian.
"In the second year, from the first day of testing, he got it into his head that there was a problem with the brakes.
"He first lost speed and then there were accidents. Suddenly you felt he was insecure. We had to react."
But promoting Verstappen to the A squad also proved very convenient in solving what Marko felt was a very unhealthy relationship at Toro Rosso, not only between the Dutchman and fellow young gun Carlos Sainz, but also between the fathers of the two drivers.
"We had Sainz and Verstappen at the same time," Marko added. "That wasn't a healthy relationship with Toro Rosso.
"On the one hand the shrewd politician Carlos Sainz Senior, on the other hand the emotional three-way Jos Verstappen. Sometimes things really got out of hand.
"With the promotion of Max, we defused it in one fell swoop. Sainz Sr. was of course offended to death and no longer understood the world.
"Internally we sometimes had to take tough action, even if things always looked harmonious to the outside world."
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