Which stars could be playing their last Aus Open?
Together they have combined for 17 Australian Open titles, held the world No. 1 ranking for more than 700 weeks and have produced countless hours of eye-popping highlights.
But will this be the last time we see them?
With the Australian Open just days away, some massive names could be hitting Melbourne Park for the final time.
From fan favourites to some of the biggest names in the game, check out the big guns who could be set for an Australian Open swansong.
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It was the announcement that shocked the tennis world.
At just 29 years of age, former Australian Open champion and world No. 1 Caroline Wozniacki declared this year's event would be her last.
And there is a simple reason the Dane has called time on her career. Her to-do list has been ticked off.
"I've accomplished everything I could ever dream of on the court," she said in a statement.
"I've always told myself, when the time comes, that there are things away from tennis that I want to do more, then it's time to be done."
Wozniacki, who turned professional at 15 in 2005, spent 71 weeks at the top of the WTA rankings.
We don't even want to think about a post-Federer era on the men's tour. But bear with us for a second because, with the Fed Express now 38 years old, we need to consider the possibility.
At first glance, it sounds crazy.
Federer is still world No. 3, won four titles last year and picked up a cool $7m in prize money.
But at this stage, what is actually left for him to achieve?
Federer won his 100th title last year and has 20 Grand Slams in his pocket.
With this being an Olympic year, a farewell tour through the major events and another shot at a gold medal could be enough for the ultimate GOAT to hang up the racquet.
Federer was quizzed on his future plans late last year.
"My retirement is going to depend on my health," he said in November. "At this moment, I see no reason to stop."
Serena Williams only has one item left on her to-do list. And that is passing Margaret Court's Grand Slam record of 24 major wins.
As she has been for the past three years, Williams sits one behind Court and could even the ledger with victory at this year's Australian Open.
Every decision she makes is now about the Grand Slams, with Williams playing just six non-major tournaments in 2019.
While she isn't talking retirement yet, at 38 years of age, it has to be on the radar. If she can pass the record this season, that may be enough for her to call time on her stunning career.
While her sister chases Grand Slam history, Venus Williams has her own milestone to tick off.
After more than two decades on the tour, Venus is just one win shy of claiming her 50th singles title.
But will she get there?
Her ranking has slipped to 54 in the world and she hasn't made it past the third round at a major since 2017.
If both sisters reach their tournament milestones this year, will they say farewell with a double retirement?
Venus will turn 40 in mid-June.
There is one massive goal driving Sam Stosur this season and it is all about Tokyo 2020.
The one-time US Open champion has her sights set on becoming just the fifth Australian to compete at five Olympic Games.
If successful, she will join Natalie Cook (beach volleyball) Mary Hanna (equestrian) Jian Fang-Lay (table tennis) and Andrew Hoy (equestrian).
While Stosur is likely to qualify for the doubles, she is also hoping to get there in singles.
The 35-year-old is coming off a tough year on the singles court, with her ranking dropping outside the top 100 for an extended period.
"I'm still playing this year coming and hopefully the year after; I haven't got any plans to stop any time soon," Stosur said in December.
It was a brutal 2019 for five-time major winner Maria Sharapova, who was stuck on the sidelines for four months after shoulder surgery. Her return didn't go exactly to plan, with the Russian knocked out of the first round at both Wimbledon and the US Open.
With her ranking now dropping to 147, where does that leave the 32-year-old's plans for the future?
"I've never had a certain goal of how long to play. When I was a young woman of 19, I'm sure I didn't think I'd be playing past 30," she said in October.
"I'm closer to the finish than the beginning or middle of my career - but who knows."
Sharapova won the 2008 Australian Open title and has finished runner up three times. She needed a wildcard to gain entry into this year's event.
THE BRYAN BROTHERS
The most accomplished doubles pairing in history has started their farewell tour.
This season will be the last on the professional tour for Bob and Mike Bryan, with the 41-year-old twins to play their final tournament at the US Open.
Together, the brothers have captured a stunning 118 titles. They have all four Grand Slams, all nine Masters 1000s and Olympic gold to their names.
"For the last 21 years, we have been so grateful for the opportunity to live out our dreams of playing professional tennis. It has truly been a magical ride," Bob said.
"However, we want to end this great ride while we're healthy and we can still compete for titles."