Michael Schumacher says he's "surprised" by Mercedes' form this campaign having spent three difficult seasons with the Brackley squad.
Schumacher joined Mercedes in 2010 but failed to win a single grand prix while his team-mate Nico Rosberg achieved just one in 2012 before the team fell woefully off the pace.
This season, though, Mercedes' have already netted three grands prix wins in just the first half.
While Rosberg won in Monaco and Britain, Lewis Hamilton, who replaced Schumacher, secured his first for the team last time out in Hungary.
"Given where we finished last season, it's a surprise where they are now," Schumacher told Eurosport.
"I could not see that coming. I'm happy for them."
The German, who won seven World Championship titles and 91 grands prix during his 19-year-old, walked away from Mercedes and Formula One in its entirety at the end of last season.
The eldest driver on the grid at the time, Schumacher admits he just didn't have the reserved needed to fight it out at the front.
"Honestly, I didn't have the strength for it, the motivation and physical strength," he said.
"These three years consumed so much energy that there would not have been enough left over to continue on the level at which I want to measure myself.
"It would not have been enough for me to win a few races. The goal of the mission was to fight for the World Championship.
"That was my mission and although this year they have done well, I had my doubts about whether I could reach my goal this year."
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