Serena and Venus Williams played against each other at a Grand Slam tournament for the first time in 1998. And guess where the match took place? At the Australian Open where they meet in the final on Saturday, with Serena the firm favourite at 1.241/4 and Venus 5.04/1.
Back in '98, elder sister Venus won in straight sets but, since then, Serena has come out on top more often than not. The younger Williams has won 16 of the sisters' 27 competitive matches. She was victorious the last time they met at a Grand Slam, winning in three sets in the quarter-final of the US Open in 2015. When it comes to career titles, Serena has 71 compared to Venus's 49.
Saturday's match will be the ninth time they have met in a Grand Slam final. Again, the younger Williams boasts by far the better record, winning six of their previous encounters.
The first all-Williams final
This was at the US Open in 2001. Twenty-one-year-old Venus came into the tournament as defending champion and swept aside opponents, including Kim Clijsters and Jennifer Capriati, without dropping a set en route to the final. Serena had a tougher time and was almost beaten by Lindsay Davenport in a gurelling three-setter. In the final, Venus retained her title in straight sets. Sixteen years on, you can get 10.09/1 on Venus 2-0 in Saturday's Aussie Open final.
The Serena Slam
Serena got her revenge when the sisters met in the final of the French Open the following year, winning 2-0. A month later, she pulled off the same feat against Venus at Wimbledon. Then, in September, Serena continued her sensational run by winning her first US Open, again in straight sets over her sister. This was the year that Serena announced herself as an extraordinary talent and she has had the edge over her big sister ever since.
There was no let-up in January when the sisters met in the Australian Open final 2003. Not that Serena had it all her own way in Melbourne. She was nearly defeated by Clijsters in the semi-final, with the Belgian 5-1 up in the third set and having two match points. In the final too, Serena had to show character, as Venus won the second set, before the younger Williams eventually prevailed 7-6/3-6/6-4 to complete the Serena Slam. You can get 3.185/40 on Saturday's final going to three sets.
A credit to sport
Following that three-setter in Melbourne, it was only six months until the next all-Williams final. They met at Wimbledon for the second year-running in 2003 and again Serena was victorious in three sets.
We had to wait another five years before they played each other again in a Grand Slam final, as the family rivalry was interrupted by, among others, Maria Sharapova. On this occasion, the All England club witnessed an upset, with Venus triumphing in straight sets. The following year, Serena got her revenge at the same venue, winning 7-6, 6-2, and that's the last time they met in a Grand Slam final.
Over the years, the Williams sisters' rivalry has been ferocious but always friendly. Both Serena and Venus will go all out to win in Melbourne on Saturday but there will be plenty of smiles and an affectionate embrace across the net at the end whoever is victorious. The Williams sisters are a credit to sport.
Tennis columnist Dan Weston's betting preview is here