Srdjan Djokovic - father to 21-time major champion Novak - was at the centre of a fresh controversy at the Australian Open when he appeared to openly support Vladimir Putin's Russia.
The former professional skier was seen alongside the 'Night Wolves' motorcycle gang, a pro-Putin chapter based Down Under who stormed Melbourne Park on Wednesday night during Djokovic's quarter-final win over Russian Andrey Rublev (watch video below).
The incident was not the first time Srdjan has caused headaches for his son.
Djokovic's Australian detention
It was a surprise to see Srdjan and wife Dijana in Melbourne at all this year, after their very public shaming of the Australian government during their son's detainment and deportation last season. Srdjan came to his son's defence in that row, but made some bizarre decisions in the process.
Last January, he and Dijana joined a protest rally in downtown Belgrade, Serbia, outside the National Assembly buildings during Novak's detention. Srdjan held a loudspeaker to encourage the crowds, and implored his son's supporters to take to the streets.
During a press conference he held in Belgrade at the time, Srdjan also called on "the Queen of Britain, Elizabeth, the leader of the Commonwealth, to intervene and protect the human rights of my son Novak Djokovic and to stop the political prosecution that has been carried out against him since he came to Australia".
He then described the Australian Prime Minister as a "dictator" and compared Novak's plight to that of Jesus Christ: "Jesus was crucified and endured many things, but is still alive among us. Novak is also crucified... He will endure".
His Federer feud
Novak was described by one of his early coaches as a "golden child" to his parents, and Srdjan has publicly worshipped his son's achievements, calling him the best player in tennis history and regularly attending the Grand Slam events to celebrate his victories.
He has also delivered some low blows to his rivals, in particular taking aim at Roger Federer. He famously got under Federer's skin in 2008 on the tennis court in Monte Carlo. Federer and a young Novak were facing each other in the semi-final that year, when the Swiss maestro turned to Srdjan in the stands and told him to "be quiet" and kicked at the baseline dirt (watch video below).
Srdjan's relationship with Federer has often been a rocky one, and he has been known to hold a grudge. He took exception to the Swiss criticising his son for calling medical timeouts during a Davis Cup match when he was 19, and brought up the episode years later too, saying Federer had "shown himself to be the best player in the world but not as a good person at that time".
Two years ago, in an interview with Serbian media, Srdjan added that Federer "is not such a good man".
While Federer and Rafael Nadal are mostly held in great esteem, Novak has not always had the same positive reception from fans. He mostly uses this to his advantage on the court, playing up to the villain persona, but Srdjan has complained about the portrayal of his son and accused the media of "defaming" him.
"It is obvious that foreign media outlets do not have the best opinion of us and think that we are constantly bothering them," he said recently. "To tell you the truth, I do not want to be part of your twisted world. I'm sorry you don't like Novak. I just tell you the truth."
Who are Putin's 'Night Wolves'?
The group Srdjan was pictured with in Melbourne are reportedly members of the Night Wolves, a pro-Russian, pro-Putin motorcycle gang which was founded in 1989 in Moscow, with groups known to be across at least 45 different countries. Putin has previously called members of the gang "friends" and made appearances at the club's rallies.
Leaders of the Australian chapter of the gang have celebrated a prominent figure like Srdjan being filmed alongside their representatives at Melbourne Park, after his son's quarter-final win over Andrey Rublev.
As well as the pro-war 'Z' emblem being displayed by these spectators and a Russia flag with Putin's face waved around, a Russian flag with the Serbian flag's insignia was also pictured at Melbourne Park. "Serbia, Russia" chants from a small group of fans echoed around the facility too.