In a rare marriage confession, Andre Agassi talks about “fighting multiple battles” with Steffi Graf.

Since their 2001 wedding, the Grand Slam tennis players have kept their relationship very quiet.

In an extremely unusual relationship confession, Andre Agassi shared the key to his 23-year marriage to Steffi Graf. The 53-year-old American tennis star and the 54-year-old German sportswoman got married in 2001, two years after splitting from Brooke Shields. Later that year, they welcomed their first child, a son named Jaden. When their daughter Jaz was born in 2003, they increased the size of their family.

Twenty years later, the couple is still occasionally featured in interviews and on social media, paying tribute to each other. This week, Andre told WSJ Magazine that the key to their strong bond is to first find happiness within. “The first is to know yourself. You can’t come to a relationship needing the other to feel complete, or else you’re fighting multiple battles,” he said.

In addition to their mutual love of tennis—Andre has won eight Grand Slam championships, while his wife has won 22 Grand Slam singles titles—they have both taken up pickleball, and in the Pickleball Slam 2, they intend to take on John McEnroe and Maria Sharapova.

The pair enjoys spending time with their kids while they’re not participating in sports. Setting aside all of their tennis trophies, devoted father Andre acknowledged that his most treasured possession is a highly heartfelt gift from his kid. “My kid made this necklace for me. These letters are beaded on a necklace. He requested me to help him when he was four years old. “I want to make this, I want to write, Daddy Rocks,” he said. We twisted these tiny beads into the letters to spell ‘Daddy Rocks.’ It broke and is being [fixed], but I’ve never taken it off,” he remarked.

Andre’s autobiography Open revealed that he had a fancy on Steffi even before they met, having won Wimbledon in 1992. He commented after watching her participate in an interview on French television: “Her subtle elegance and effortless beauty left me speechless. After the French Open in 1991, I attempted to message her, but she did not reply.” Before their romance developed some years later, they went on to date separate people: Agassi’s relationship with Brooke started in 1993, while Steffi’s relationship with Michael Bartels lasted from 1992 to 1999.