McLaren's Lewis Hamilton had to fight back tears as he discussed his impending departure from McLaren.

Hamilton's last race with the team which has supported him since he was 13 is Sunday's Brazilian Grand Prix. He joins Mercedes for 2013.

Asked by BBC Sport how he will feel after the race, the 27-year-old said: "I might have to keep my helmet on.

"It's going to be tough. It's my family and I'll be going elsewhere. It's best I don't talk about it too much."

quote I really feel as if I'm leaving my home and going elsewhere

Hamilton's eyes then welled up. BBC pit-lane reporter Lee McKenzie said: "You get choked up thinking about it?"

Hamilton replied: "Mmm."

He said of his girlfriend Nicole Scherzinger: "My missus is always telling me every bit of time is precious and I'm going to maximise the time I have this weekend."

The 2008 world champion said making the decision to join Mercedes, which he did while on holiday in Thailand after the Singapore Grand Prix at the end of September, had been a weight off his shoulders.

"It started getting more and more intense with the questions every weekend - when are you going to do this, where are you going to go?" he said.

"Every weekend and then the last month or so was horrible.

"I had that pressure on and in my personal life when I'm stressed I don't know how to get it out of me, and I was very stressed and then I had to do my job.

Hamilton's career Makes his debut in 2007 at the Australian Grand Prix for McLaren, qualifying fourth and finishing third

Wins the 2007 Canadian Grand Prix after finishing on the podium in each of his first five races

In 2008 signs a lucrative five-year contract to race for McLaren until the end of the 2012 season

The same year he becomes, at the time, F1's youngest world champion

A disappointing 2009 sees him finish fifth with only two wins

Still searching for his second World Championship title after finishing fourth and fifth in 2010 and 2011 respectively

Signs to race for Mercedes from the 2013 season

"I had to still perform, and also my auntie passed [away] which was really the toughest couple of weeks, three weeks we had as a family because we hadn't had anything like that happen to us before. It was just a really horrible period of time.

"And when I finally sat down, I was sitting down in Thailand. And I'd gone there to go for the week with Nicole, but it didn't work out that way, and I went there for a literally a day and I was just sitting by the pool thinking about life and I was just able to release, and it was: 'This is what I want to do.'

"It became clear that I wanted to try something new and I was going to go for it. And then I called Martin [Whitmarsh, McLaren team boss].

"It was the most difficult call I've ever had to make because we'd grown so close and he had been so supportive and I didn't want to let people down.

"But at the end of the day you have to let people down sometimes to make decisions."

He said he would still be leaving even if he had won more than one world title with McLaren.

"I think so - six years is a long time, 15 years is a long time. This is not… I don't see it as… when someone leaves a job, I don't see it like that.

"I really feel as if I'm leaving my home and going elsewhere. I've learnt my skills and I've got all the right skills to go out and try something different."

Hamilton admitted he had found the pressures of life in F1 difficult to deal with at times during his career.

"In F1 things do change a lot," he said. "Before I was just there to race but then in F1 everything changes. Media, pressure from sponsors, money, fame - all these things come into it.

"They're thrown into one pot and you don't know what's going on and it's definitely taken a while to grow up and grow into it, which I still feel I'm doing.

"But I feel I've been at my best I've been so far both on the driving side but also in my personal life."

He added: "It wasn't my target to have a glamorous girlfriend but it just so happened that I had the biggest crush on this girl and I happened to meet her. And it was like - you're not going anywhere!"

He said he had no regrets about his decision to join Mercedes, who have failed to score a single point since Hamilton's decision was announced.

"I have to trust my decision. It is what it is," he said. "I made it; I stick to it.

"I don't for one second think: 'Oh, I wish I didn't.' I feel: 'Right, when my job is done here, how am I going to turn that car around?'

"I've studied everything about it. I know how it looks. I know it doesn't look right. There are going to be things they do better than McLaren and there are things we do that will be better than them and I'll hopefully be able to string both of those together."