Fekitoa signed a two-year deal with the Top 14 side, confirming the deal via his Instagram page last month.
The 24-Test player spoke for the first time on Thursday about his decision to leave, revealing a slip down the pecking order with the All Blacks was the main decision to leave.
"It was the hardest decision I have ever made," Fekitoa told reporters.
"I just started my career and even though 90 percent of fans and supporters disagree with it I believe it is the right to do that and I think it will make me a better player.
"I am a starter. That is me as a rugby player and I always want to be number one and you think that if you can't have that then why hang around and be a third or fourth choice.
"I can't control that but what I can control is my career and this weekend game so I do well I am happy with that."
But before Fekitoa departs to the South of France, the World Cup winner will play for Auckland during this year's Mitre 10 Cup.
Fekitoa last played for Auckland in 2013 and he hopes to lead the province to their first domestic title since 2007.
"This is where it all started and it is good to back and go back to the club. I think it is good to come back here and help the young players.
"I want to win the championship for the club as it has been 10 years. I can't talk a lot but I'll lead by example and have fun and enjoy my time at the club."
However, we might not have seen the Fekitoa who said he plans to return to New Zealand in the future.
"I don't know when, but I will be back."
Fekitoa will join former All Blacks Ma'a Nonu and Luke McAlister at Toulon at the conclusion of the Mitre 10 Cup season.
He will start at centre on Saturday night when Auckland face Counties Manukau in their first match of the season.