It is safe to say 19-time grand slam champion Rafael Nadal and outspoken Australian Nick Kyrgios are not friends.
Their feud stems back to February last year and shows no signs of subsiding ahead of Monday's last-16 showdown at the Australian Open.
As the pair renew hostilities in Melbourne, we look at the timeline of events that has led to tennis' biggest feud.
February 2019 - Sparks fly in Acapulco
Kyrgios' first meeting with Nadal was at the All England Club in 2014 - the then-19-year-old Kyrgios stunning the two-time Wimbledon champion to reach the quarter-finals.
However, their Mexican Open date five years later changed things completely. Kyrgios took down Nadal in the second round en route to winning the ATP Tour tournament. Kyrgios was at his brilliant and menacing best, rallying from a set down, saving three match points and attempting underarm serves. He also complained that Nadal was taking too long to serve.
Afterwards, Nadal told reporters: "He's a player who has enormous talent, could be winning grand slams or fighting for the number one ranking. He lacks respect for the crowd, his opponent and towards himself… I don't think he's a bad guy, but he lacks a little respect for the public and the rival."
Kyrgios responded by saying: "He doesn't know anything about me. So, I'm not going to listen at all. That's the way I play. The way he plays is very slow in between points. The rule in the book says he has to pay to the speed of the server, but Rafa has his speed every time, so I'm not going to comment on him. He's got his own game. I've got my game. We played well. That's the sport. People are different so I'm not going to take that into consideration at all."
March 2019 - Uncle Toni takes aim at Kyrgios
At Indian Wells, Nadal tried to quell what he said, but his uncle Toni reignited the fire as he got involved.
In an interview with Radio Marca, Toni Nadal said: "Rafa is totally right. He [Kyrgios] lacks education and smartness. He should be fighting for the top rankings and instead, he is number 40. He does not look like a bad guy but he has been disrespectful too many times to get back on track."
May 2019 - Kyrgios returns serve as war of words continue
Never one to sit back and hold fire, Kyrgios responded in his appearance on podcast 'No Challenges Remaining' as the maligned Australian ruffled feathers ahead of the French Open.
Describing Nadal as "salty", the unfiltered Kyrgios told tennis writer Ben Rothenberg: "When he wins, it's fine. He won't say anything bad, he'll credit the opponent, 'He was a great player'. But as soon as I beat him, it's just like, 'He has no respect for me, my fans and no respect to the game'.
"It's not a good look for you, I feel. And then uncle Toni came out saying, 'He lacks education'. I'm like, 'Bra [brother], I did 12 years at school, you idiot. I'm very educated. I understand that you're upset I beat your family again'."
July 2019 - Kyrgios and Nadal reunite at Wimbledon
Fans and pundits were licking their lips when Kyrgios and Nadal went head-to-head in the second round of Wimbledon. Nadal emerged triumphant in four sets after an eventful and tense battle. Kyrgios served underarm, received a code violation for unsportsmanlike behaviour and hit the unimpressed Nadal with a powerful forehand.
Asked if he regretted not apologising for hitting Nadal, Kyrgios responded: "Why would I apologise?… I didn't hit him. Hit his racquet, no? Why would I apologise? I won the point."
"I don't care. Why would I apologise? I mean, the dude has got how many slams, how much money in the bank account? I think he can take a ball to the chest, bro. I'm not going to apologise to him at all," Kyrgios added.
"I was going for him. Yeah, I wanted to hit him square in the chest. Like, he's got decent hands."
January 2020 - Kyrgios impersonates Nadal as tension builds
Fast forward to the Australian Open and Kyrgios has already added more spice to a tasty fourth-round matchup. Kyrgios impersonated Nadal as he was called for a time violation during his win against Gilles Simon in the second round at Melbourne Park.
When asked if he liked Kyrgios following Saturday's routine victory over Pablo Carreno Busta, Nadal's response was telling. "I don't know. I don't know him personally, honestly, to have a clear opinion," Nadal told reporters. "It's clear, of course, that when he does stuff that in my opinion is not good, I don't like.
"When he plays good tennis and he shows passion for this game, he is a positive player for our tour, and I want my tour bigger, not smaller. So the players who make the tour bigger are important for the tour. When he's ready to play his best tennis and play with passion, is one of these guys. When he's doing the other stuff, of course I don't like."
After earning a date with Nadal courtesy of a marathon five-setter, Kyrgios said in a news conference: "At the end of the day, we're two different tennis players. We go about it completely different… Regardless, if we don't like each other or whatever, I think there's a layer of respect. He's one of the greatest of all time.
"I also read that he thinks I'm good for the sport. There's a layer of respect that we both have for each other. Doesn't necessarily mean we like each other, but we're going to go out there and give contrasting styles and personalities.
"I don't really know Rafa. I've never hung out with him or anything like that. So I don't really know how he is. I don't really dislike him. I don't know him at all. Hell of a tennis player. Don't know him as a person. I'm sure he's okay."