Christian Horner is sad to bid farewell to Red Bull's Daniel Ricciardo

Christian Horner admits he is sad that Daniel Ricciardo has left Red Bull.

The team boss said Australian Ricciardo alongside Max Verstappen was "the best duo in the history" of the energy drink owned outfit.

Mutual respect

Ricciardo shocked both Red Bull and the rest of the Formula 1 world by announcing his move for 2019 to Renault.

READ: Ricciardo denies wanting 'too much money' from Ferrari

"There was a momentum and respect between the two that meant they kept pushing each other to the limit," Horner said, referring to Ricciardo and Verstappen.

Red Bull initially placed Ricciardo at HRT in 2011, before he got a promotion first to Toro Rosso and then Red Bull Racing.

"We never worried about Daniel's pace," Horner told RTL, admitting that the big worry was about Ricciardo's ability to go wheel-to-wheel.

"Now he is one of the best drivers in the field when it comes to overtaking. His personality was also a perfect match for our brand."