Coach Patrick Mouratoglou, rumored to be Serena Williams' boyfriend, is all praises for the women's tennis world's no. 1.

He told Sky Sports News that to win four Grand Slams in today's environment where the competition is very steep is "an incredible achievement."

"Winning just one Grand Slam for anyone is such a big achievement," he added.

Serena Williams won the recent Wimbledon Championship 2015 and her rumored boyfriend Patrick Mouratoglou said that the tennis ace "had such a tough draw, playing Heather Watson, Venus [Williams], Vika [Azarenka] and [Maria] Sharapova."

The draw was so difficult, she had so many tough matches, but she made it every single time against every kind of adversity," he added. "She faced different game plans, different kinds of tennis, being sick, not feeling great every day."

Patrick Mouratoglou continued, "It's incredible to be able to focus and show so much dedication and ability to turn things around when you are in trouble."

Previously, the world's number one shared a photo on her Instagram showing her in a white gown standing alongside rumored boyfriend Patrick Mouratogloue while they held up the Wimbledon trophy.

She captioned the image, "So happy @patrickmouratoglou could make this #Wimbledon dinner. He missed the last. Thanks Patrick for your perseverance and non stop belief and faith in me. #renasarmy #SerenaSlam 2.0 #ontothenextone."

The two have been rumored to be dating, although the tennis ace in the past has insisted that she's single. At one point, Serena Williams was also rumored to be hooking up with rapper Drake. Serena Williams has been the subject of nasty body shaming online after a few people suggested that she only won because of her manly physique.

Serena Williams will again attempt the rare feat of winning four majors in a single year and her next challenge, along with her rumored boyfriend coach, is to win the US Open in September.