Simona Halep has been labelled an illegitimate World No.1 because she hasn't won any grand slams.
But Roger Federer just put all the haters in their place.
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Romanian Halep will finish 2017 as the women's World No.1, pipping fellow contenders Garbine Muguruza, Karolina Pliskova, Elina Svitolina, Caroline Wozniacki, Venus Williams and Jelena Ostapenko.
Halep was destroyed 6-0, 6-2 in the early stages of the WTA Finals in Singapore by Wozniacki, but other results saw her secure the top ranking.
Halep is the seventh women's player to go No.1 without a slam, joining Kim Clijsters, Amelie Mauresmo, Jelena Jankovic, Dinara Safina, Pliskova and Wozniacki.
But despite the momentous achievement, the 26-year-old has run into plenty of criticism over the fact that she's No.1 despite failing to win a grand slam in her career.
On Tuesday, she received some high praise from none other than Swiss legend Federer, who came out firing in support of Halep.
"Not for a second should you ever take away anything from Halep, who's worked their life to achieve a life-goal dream," Federer said after winning the Swiss Indoors in Basel.
"It's not only about grand slams.
"She's played a full season. She's tough, fit, playing all the time, she practices hard, she's committed and that also should be rewarded.
"I am really happy for her and excited to follow the women’s game until the very end because there were so many players who could finish No.1."
Halep got wind of Federer's comments and was quick to thank him.
"I felt really proud of myself that Roger Federer could talk about me like that, I thank him for the nice words," Halep said.
"He is one of my (role) models."
Pliskova, who was No. 1 earlier this year, agreed with Federer.
Halep came perilously close to winning her maiden slam when she was defeated by Ostapenko in the French Open final.