Lewis Hamilton is struggling to comprehend the loss of Niki Lauda after the three-time Formula One world champion died on Tuesday.
Lauda, who served as Mercedes' non-executive chairman since 2012, has passed away at the age of 70.
The Austrian was credited with helping Mercedes succeed in their pursuit of Hamilton when he was contemplating leaving McLaren seven years ago, and was present for many of his successes from then on.
Hamilton, 34, has won four of his five world titles while with Mercedes and expressed his sadness after the loss of one of the sport's greats.
"I'm struggling to believe you are gone," Hamilton wrote on Twitter.
"I will miss our conversations, our laughs, the big hugs after winning races together. God rest your soul.
"Thank you for being a bright light in my life. I'll always be here for your family should they ever need me. Love you man."
Hamilton's team-mate Valtteri Bottas and Mercedes boss Toto Wolff also paid tribute to Lauda earlier in the day.