Christian Horner says he understands Sebastian Vettel's decision to leave Red Bull Racing, as the "lure of Ferrari for any driver is immensely powerful."

Vettel has signed a three-year deal with Ferrari following Fernando Alonso's exit from the Italian team, ending a relationship with Red Bull's motorsport programme that had been in place since the German was 12 years old.

Vettel won four world championships with the Milton Keynes-based outfit between 2010 and 2013, becoming only the fourth man in history to do so.