Sloane Stephens Is Learning Spanish from Her BFF Rafael Nadal: 'Rafa's the Best!'

Masha Maltsava/Lemon Perfect Sloane Stephens

Sloane Stephens is building her resume of accomplishments both on and off the court!

While the 2017 US Open champion, 29, has had quite the packed schedule this year, she told PEOPLE recently that she is sure to make time to pursue her passions and interests outside of tennis and even recruiting the help of some friends.

When asked about a recent photo shared to Instagram of the tennis star posed with Rafael Nadal captioned, "With my bestie," Stephens said her friend is helping improve her language skills.

"Rafa is the best!," she told PEOPLE.  "He's helping me learn Spanish. I've spent time training in Spain for 15 years and most of the kids my Foundation works with speak Spanish at home, so it is time."

Stephen's foundation, the Sloane Stephens Foundation, is another one of the interests she is pursuing off the court.

The organization's mission on their website reads, "We use tennis and education to change the narrative of poverty, health inequity, and educational underdevelopment."

The tennis player has also joined the likes of Beyoncé as an investor in Lemon Perfect, a hydrating lemon water company. Stephens said the company has been "a huge supporter" of her organization's mission and has committed showing their support monetarily as well.

Masha Maltsava/Lemon Perfect Sloane Stephens

"[Lemon Perfect founder] Yanni Hufnagel and I bonded over our shared beliefs in the power of wellness, education and making people happy right from the start," she said. "Through our partnership, Lemon Perfect has committed to donating $5,000 per year to my Doc & Glo Scholarship [founded in honor of her late grandparents] and it means a lot to have that support."

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Stephens shared that though she's best known for her incredible skills on the tennis court, she's passionate about seeking what excites her off the court as well, from entrepreneurship to newlywed life.

"Tennis has opened up so many doors in life and shown me how much is possible," she said.  "Being a professional tennis player is my day job, but it is not the entirety of how I see myself each day. By having outside interests, projects, and investments, I can explore those parts of me, and continue playing tennis without feeling like it is the only thing I do."

This time of the year, though, is all about tennis as the U.S. Open is underway — an event Stephens called "one of the highlights of every season."

"It's great being back in New York," she said.  "I have so many family and friends who have these dates circled on their calendar all year, and it's nice to have that support."

Vincent Ethier/Icon Sportswire via Getty Sloane Stephens

At the beginning of the year, Stephens celebrated another off-the-court milestone when she wed soccer star Jozy Altidore on New Year's Day. At the time, Stephens told PEOPLE their relationship was an anchor for her: "We both have incredible crazy jobs and lives, and knowing that through it all, we have each other as our constant and true home base is such a comforting feeling."

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And she still feels the same way nine months later, as their schedules haven't slowed down enough to let them take a honeymoon; Altidore has been "on loan" to the Club Puebla professional soccer team in Mexico and she's been competing, though they hope to take a "mini-moon" in December when they're both in their off seasons.

"When you travel 40-plus weeks a year for work, all you want to do is come home to each other and enjoy the down time," she said. "We definitely will take a honeymoon at some point, but we're both super busy with work!"

Stephens won her round one match this year's US Open against Belgium's Greet Minnen on August 30 and takes on Iga Swiatek Thursday in round two.