One secret to Elton John and David Furnish's lasting relationship? Handwritten love letters. The couple have been penning and sending each other personal notes every week for the past 25 years, they revealed in a new video from R&B artist 6LACK's (pronounced "black") confessional series about love. "Every Saturday, we gave each other an anniversary card, because we met on a Saturday," Furnish tells 6LACK in the clip."So we wrote down, in like a little card that you put next to the bed, 'Happy Anniversary,'" he continued, "And you write about the week that's passed and the week that's coming, and you connect and you tell each other you love each other."No matter where they are in the world, John and Furnish send their weekly cards via courier. If delivery would take too long due to extreme distances, it's no problem; they'll fax the notes instead. "Every Saturday, without fail, in the last 25 years, we've sent each other a card or a fax," John assures. What's most important to the couple is that, no matter how the message is sent, it still appears in writing. "It's not quite the same as a text or an email," Furnish explains. "I think seeing the handwriting on paper and feeling the person's humanity through that, and the fact that we do it religiously every Saturday, has been a very powerful bonding thing for us." All of the opened and read cards are kept in a safe in the couple's home. "It's a whole catalogue of our relationship," Furnish says. That includes the bad days, too. "We sort through by communication, and one way of communicating is writing down on a piece of paper or card how you're feeling," adds John.Furnish and John met in 1993, married in December 2014, and currently have two sons together. Furnish and John are just two of the many who participated in 6LACK'S video campaign, featuring fans and celebrities answering in-depth questions titled "Can I Ask You a Question About Love?" Fans can participate by recording their own confessionals on eastatlantaloveletter.com.