The on-again, off-again, never-confirmed relationship between Serena Williams and coach Patrick Mouratoglou could be on again, according to a report.

Daily Mail Australia reported earlier this week that Williams, the No. 1 female tennis player in the world, and Mouratoglou, who has been her coach since the summer of 2012 and may have been her boyfriend soon after, were spotted looking very comfortable together in an airport in Perth, Australia, over the weekend.

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Williams currently is playing in the Hopman Cup, a tuneup for the season's first Grand Slam event, the 2015 Australian Open that begins on Jan. 19.

The Daily Mail website provided a few pictures of the two together - the one catching the most attention being a selfie in which the two huddled close together. You can see the photos of Williams and Mouratoglou here.

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The photos don't offer any concrete proof that Williams and Mouratoglou are together, and for her part, Williams has gone to great lengths to deny anything more than a coach-student relationship exists.

As recently as September, Williams went on her Twitter account in an attempt to dispel rumors of their relationship, saying, "To answer all your questions, I'm single and I have been single so the speculations can stop."

The speculations began with a war of words between Williams and Maria Sharapova in 2013. Sharapova began dating Grigor Dimitrov, who was rumored to be a past boyfriend of Williams. In an interview with Rolling Stone magazine, Serena talked about an "unnamed" top-five player that was assumed to be Sharapova, and said that the player's boyfriend had a "black heart."

Sharapova fired back in a pre-Wimbledon news conference, accusing Williams of dating a married man with children, which was presumed to be a reference to Mouratoglou.

Williams and Mouratoglou were rumored to have broken up at Wimbledon after Williams' bizarre on-court behavior in a doubles match with sister Venus. She claimed to be sick, while Mouratoglou reported he hadn't talked to her in two days and admitted she was going through a "difficult" time. Williams had lost her third-round singles match just a couple of days before her infamous doubles match.

Williams rebounded to win the U.S. Open.

Despite Williams' insistence that she is not dating Mouratoglou, she has been largely unsuccessful in convincing the media - established, social or otherwise.

And the photo of the two taking a selfie do nothing to help Serena's claims of a platonic relationship.