Lewis Hamilton says his decision to leave McLaren for Mercedes at the end of 2012 was “one of the most difficult moments” on his Formula 1 journey.

The Briton opted to end his long-term partnership with McLaren in order to join the Mercedes works team for the 2013 season at a time when Mercedes had won just a single race since returning to F1 as a works operation in 2010.

Hamilton’s decision to cut ties with the team he had claimed his maiden world championship and won 21 races with in order to make the switch to a then-struggling Mercedes outfit led many people to question whether he had made the right move for his career.

But Hamilton has proved any doubters wrong by racking up five world championships and 70 wins in six seasons and being on course to match Michael Schumacher’s all-time benchmark of seven drivers’ titles by the end of the year, having equalled the German’s record of 91 race victories last time out at the Eifel Grand Prix.

“I think it’s pretty impossible to say what is the hardest moment because like all of us, all of us as individuals, we all go through multiple difficult moments, particularly when it comes to making big decisions,” Hamilton replied when asked what he felt had been his hardest moment on his journey to 91 wins.

“Whilst it looks great now, when choosing to move to Mercedes, everyone spoke so negatively about the decision to move. I knew that it was the right decision for me and I wanted to be a part of that journey.

“I’ve grown with a team that’s hungry for success but I would say that’s one of the most difficult moments, because I’d been a very loyal person.

“I was with McLaren-Mercedes since I was 13 so to decide to leave a team that’s given me a place in the sport was very, very difficult for me and to call your boss and tell him that you’re leaving, it was damaging and just emotionally difficult.

"But then I’m still with Mercedes, every win and every race that I’ve done has been powered by Mercedes and for that I’m incredibly grateful.”

Hamilton said that informing then-McLaren team principal Martin Whitmarsh of his decision to leave the team was a particularly difficult moment.

"Calling my boss, calling Martin in particular, was one of the hardest calls that I've ever had to make," he explained.

"I hope that he has forgiven me by now! I think so, because he understands, but ultimately I think it was the right decision.

"Without their support, along with Mercedes, I wouldn't have made it to Formula 1, being that it is so expensive so there was no way, as family, that we had the sorts of money that some other families are able to throw at this sport,” Hamilton added.

"So my loyalty was to them, but at the time, I had to think about what the future would hold and what I wanted to be a part of.

"I wanted to be a part of a team that perhaps hadn't had as much success, was in the growing phase, and I wanted to be a part of that, that growing journey, building something relatively new.

"That was an exciting challenge and I didn't know how long it was going to be until we got to winning ways. But I truly, truly believed that we would get there at some stage."