By alley - Dec 2, 2016, 11:29 AM ET

F1: Rosberg decision no surprise for Hamilton

Lewis Hamilton was not surprised to hear of Nico Rosberg's

retirement from Formula 1

, saying he knew how much it would mean for the German to beat him to this year's world championship.

Rosberg won his first drivers' title in Abu Dhabi on Sunday, finishing second to Hamilton in the race to win the championship by five points. On Friday in Vienna, Rosberg then surprised many in F1 by announcing his retirement from the sport with immediate effect, saying he is not willing to continue making the required sacrifices to defend his title.

Hamilton, however, says he was not shocked by his teammate's decision, having raced against him on a number of occasions in karts and junior categories before being paired at Mercedes.

"I'm sure it was a surprise to many people," Hamilton said. "I'm probably one of the many people that it was not a surprise for but that's because I've known him for a long, long time. But this is motor racing.

"This is the first time he's won in 18 years, hence why it was not a surprise that he decided to stop. But also he's got a family to focus on and probably wants to have more children. Formula 1 takes so much of your time.

"In terms of missing the rivalry, of course because we started karting when we were 13 and we would always talk about being champions. When I joined this team Nico was there which was something we spoke about when we were kids so it's going to be very, very strange and for sure it will be sad to not have him in the team next year."

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However, Hamilton himself says he would not have walked away from the sport as the reigning drivers' champion, as he would feel the need to defend it the following season.

MEDLAND: Was Rosberg's retirement really a shock?

"Of course it is a shame that he won't allow me to take it back or fight me to take it back, but that's obviously his choice and I respect his decision. Go out on top while you can. I have a different viewpoint, I won the championship in the past two years and I gave an opportunity each year for someone to have another shot at it.

"That's generally how I am; I consistently believe in my ability and what I can do each year, so even if I was to win again most likely I would give another opportunity. I love racing, I love going out there and being challenged by different competitors. We've been racing for 18 years so it's not the worst scenario for me."