He delivered the first upset at Wimbledon on Monday. (AP)

Roger Federer delivered the most shocking upset on Day 1 at Wimbledon by appearing in a Uniqlo outfit. After weeks of speculation, it's official: He's not a Nike man anymore. 

"I was excited to wear Uniqlo today. I must tell you, it's been a long time coming," Federer said. "I felt very good out there. It's also crucial to play well, so it was helpful."

No one was sure of what brand he would wear at the All England Club, especially since he wore a suit for his pre-tournament press conference. 

People were a little surprised, to say the least:

The reported deal is for 10 years and worth upwards of $300 million, and he will be paid even if he's not on tour. Before Federer, Kei Nishikori was the biggest name wearing the Japanese brand, which is most well-known as a casual wear brand. Novak Djokovic was with Uniqlo previously, but he switched to Lacoste in 2017. Federer is still representing the Nike swoosh on his shoes. 

The shoes are, as always, extra special for Federer:

But even those may change, as he doesn't technically have a shoe deal: 

"With the shoe situation, I don't have a shoe deal. I'm looking forward to see what shoes I will be wearing in the near future," Federer said. "For now, I will be wearing Nike. They have shown interest to have a shoe deal with me, as well. Ties are not broken there. I have deep roots with Nike. I've had a great relationship over the last 20 years. But everything is open."

Federer has been with Nike since 1994, well before his career took off, and he built a popular brand, RF, over the years. His RF logo will revert back to him at some stage in the future.

"So the RF logo is with Nike at the moment, but it will come to me at some point," Federer said. "I hope rather sooner than later, that Nike can be nice and helpful in the process to bring it over to me. Look, it's the process. But the good news is that it will come with me at one point. They are my initials. They are mine."

Last month, he said his Nike contract had ended in March but he didn't confirm anything until stepping on court for his first match on Monday against Dusan Lajovic. 

A press release was provided, stating the 20-time Grand Slam champion will wear Uniqlo at tournaments throughout the end of the year.

“I am deeply committed to tennis and to winning championships. But like Uniqlo, I also have a great love for life, culture and humanity," Federer said. "We share a strong passion to have a positive impact on the world around us and look forward to combining our creative endeavors.”

Federer breezed into the second round over Lajovic, 6-1, 6-3, 6-4. 

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Strokes of Genius is a world-class documentary capturing the historic 13-year rivalry between tennis icons Roger Federer and Rafael Nadal. It is timed for release as the anticipation crests with Roger as returning champion, 10 years after their famed 2008 Wimbledon championship – an epic match so close and so reflective of their competitive balance that, in the end, the true winner was the sport itself.