Novak Djokovic engaged to longtime girlfriend

(CNN) -- It's a love match for Novak Djokovic.

Tennis' world No. 1 announced his engagement to longtime girlfriend and fellow Serb Jelena Ristic, telling the world via his Facebook page and Twitter.

"Meet my fiancée and future wife :) So happy! Thank you for wonderful wishes #NoleFam and friends!"

Accompanying that tweet was a picture of Ristic kissing Djokovic on the cheek.

No wedding date was given.

Djokovic has been dating Ristic for about eight years. She is a regular in his box at major tournaments around the world and has modeled swimwear.

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But Ristic also obtained a master's degree in Luxury Management from the International University of Monaco and is the CEO of the Novak Djokovic Foundation.

"We are emotional partners," Ristic told Britain's Daily Mail in July. "The emotional support we give to each other is very important.

"It's the same for me as well. He is very supportive and encouraging of the work that I do."

Only one member of the 'Big Four' in men's tennis, Roger Federer, is married.

Like Djokovic, though, Rafael Nadal and Andy Murray have been dating their girlfriends -- Xisca Perello and Kim Sears, respectively -- for many years.

Djokovic's engagement comes days after he hit 100 weeks as No. 1, although he'll likely lose the top ranking to Nadal during the current Asian swing.

Djokovic and Nadal are competing at next week's China Open in Beijing.

Caroline Wozniacki is in the women's draw in Beijing -- and her high-profile relationship with golfer Rory McIlroy made news last month.

An Irish newspaper reported that the former No. 1s in their respective sports split, although Wozniacki subsequently tweeted a picture of the two having breakfast together.

McIlroy, too, watched the Dane compete at the U.S. Open in New York.