They speak different languages and are total contrasts in appearance and character. One has a robust frame and is a bright and bubbly personality who wears her heart on her sleeve. The other, a slight figure, is a thoughtful and quietly spoken individual who jealously guards her private life. While the former happily lives in her home country, the latter has chosen the relative anonymity of Monte Carlo.
Yet two facts will for ever link Kim Clijsters, 23, and Justine Henin-Hardenne, 24. They are both Belgian and world-class tennis players. After meeting on numerous occasions as juniors they have already played each other 21 times as professionals. Today they meet for the first time at Wimbledon, with a place in Saturday's final at stake.
The parallels between their careers are remarkable. They grew up as the best players of their generation in Belgium (a country hardly renowned for producing tennis talent) and broke into the world's top 100 in 1999 and the top 10 two years later. Clijsters, from the Flemish-speaking part of the country, became world No 1 in August 2003. Henin-Hardenne, from French-speaking Liège, became top girl two months later.
They even suffered major health problems at around the same time. In 2004 Henin-Hardenne went down with cytomegalovirus, a debilitating illness which laid her low for 18 months (although in one brief comeback she won the Athens Olympics title). Clijsters, the early part of her year disrupted by an ankle injury, had surgery on her left wrist in June 2004.
Both made phenomenal comebacks the following year. Clijsters won nine titles, including her first Grand Slam event, the US Open, while Henin-Hardenne won 24 matches in a row on clay and successive titles in Charleston, Warsaw, Berlin and Paris.
While Clijsters has the edge in prize-money and tournament victories - she has won $13.5m (£7.4m) and 31 singles titles compared to Henin-Hardenne's $11.4m (£6.2m) and 24 titles - her rival has won five Grand Slam crowns. Wimbledon is the one major Henin-Hardenne has yet to conquer, although she has already appeared in one final and two semi-finals. Clijsters, whose best Wimbledon run took her to the 2003 semi-finals, had lost in four Grand Slam finals before lifting the US Open last summer.
Both players insist that theirs is a friendly rivalry, but it is clear that they are far from close. For a while they did not play together for Belgium in the Fed Cup, although there was a much publicised reunion when they made a winning return against Russia earlier this year.
The paths of the two girls first crossed when Clijsters was eight and Henin-Hardenne nine. The outstanding Belgians of their age, they faced each other in the semi-finals of a summer tournament in Ostend. Their match drew a sizeable crowd, with Flemish supporters lining up on one side of the court and French speakers on the other. Henin-Hardenne won the first set without losing a game, at which point Clijsters retired hurt. Henin-Hardenne's father questioned whether Clijsters was injured and recalled that she went on to play doubles later that day.
The two players represented Belgium at Under-14 level and often shared hotel rooms. When Henin-Hardenne was 16 they teamed up to win the doubles in an International Tennis Federation event in Israel.
As seniors they first met in 1998, Henin-Hardenne beating Clijsters in straight sets. Henin-Hardenne won again in Reims the following year, but it was the younger woman who got the upper hand after winning in Indian Wells in 2001, taking seven out of nine matches against her great rival, including two in Grand Slam tournaments. Since then the pendulum has swung back, Henin-Hardenne winning seven of their last 10 meetings.
Clijsters, who says Henin-Hardenne is "by far the best clay-court player in the world", says she will attack when they meet today. Clijsters said: "She's worked a lot on her strength. She hits a lot more powerfully than she used to. I have to be aggressive, make sure that I keep it up." Henin-Hardenne says Clijsters is a "complete player" who can win on any surface. "She's a very powerful player. She's moving well, and she has great qualities. She's a champion."
Clijsters is universally popular within the sport and a smile is rarely off her face. She is also acknowledged as one of the most sporting of players. Against Li Na in the quarter-finals here, Clijsters told the umpire to over-rule a line judge's "out" call on her opponent's serve, costing herself the point.
In contrast, Henin-Hardenne's motives on court have sometimes been questioned. There was widespread criticism of her in the final of this year's Australian Open final, when she retired when a set and 2-0 down to Amélie Mauresmo, complaining of stomach pains. Many felt that she had denied Mauresmo the chance to enjoy fully her first Grand Slam title.
Clijsters herself made critical comments about Henin-Hardenne after they met in the final of a tournament in San Diego three years ago. Henin-Hardenne took an injury time-out for treatment to blisters at an important stage of the match.
Claiming that Henin-Hardenne had regularly called for the trainer during matches against her, Clijsters said: "It didn't look like it was hurting. I think she was still running quick. I don't want to say anything bad about her, but it's not the first time that's happened. Those are moments that you know that she's not feeling her best and she has to try to do different things."
Clijsters later insisted that she had not intended to suggest that Henin-Hardenne had feigned injury. At the time Henin-Hardenne had replied: "She can think whatever she wants. I have no problem with my actions, not at all. When you're not in this situation you cannot understand what it is to play with a blister."
That year their relations seemed to reach an all-time low after Henin-Hardenne beat Clijsters in the final of the US Open. When the winner returned to Brussels she was immediately questioned by reporters about comments made by Leo Clijsters, Kim's father, who had suggested that Henin-Hardenne's power could not be explained simply by work in the gym. Henin-Hardenne said she had nothing to hide. "It's thanks to my hard work and combative nature that I've achieved these results," she said.
Henin-Hardenne's family life has been a mystery. She was very close to her mother, who died of cancer when she was 12. At 17 Henin-Hardenne left the family home for good and cut off all ties with her father and two elder brothers. The reasons have never been made public.
When she married Pierre-Yves Hardenne in 2002 after a four-year romance, the only members of the Henin family who attended the wedding were two aunts. She did not invite her father, two brothers, sister, grandparents or paternal uncles. There has been some recent contact with her father and sister, but Henin-Hardenne generally seems happy with her own private world comprising her husband and Carlos Rodriguez, her coach since 1996, and his family.
In contrast, Clijsters' personal life has been led in the public eye. A romance with Lleyton Hewitt ended within weeks of their planned wedding and she is now engaged to Brian Lynch, a basketball player. Clijsters says she will retire at the end of next year.
Today both players insist they have no problem with each other. "We came back together in the Fed Cup," Henin-Hardenne said. "We've been very professional adults about that. There's a lot of respect between each other." Clijsters says:"We get along. People automatically think that because you beat each other a few times it creates tension or something. But I've never felt that. I don't know about her, but I've never felt that."
Henin-Hardenne v Clijsters
Justine Henin-Hardenne and Kim Clijsters have met 21 times as seniors, Henin-Hardenne winning on 11 occasions. They have met six times in Grand Slam tournaments:
2001 French Open semi-final (clay): Clijsters won 2-6, 7-5, 6-3
2002 Australian Open quarter-final (hard): Clijsters won 6-2, 6-3
2003 French Open final (clay): Henin-Hardenne won 6-0, 6-4
2003 US Open final (hard): Henin-Hardenne won 7-5, 6-1
2004 Australian Open final (hard): Henin-Hardenne won 6-3, 4-6, 6-3
2006 French Open semi-final (clay): Henin-Hardenne won 6-3, 6-2