Serena and Venus Williams will play each other for the 26th time when they meet in the fourth round at Wimbledon on Monday.

A match involving Williams vs. Williams used to be a regular occurrence at the latter stages of the most prestigious tennis tournaments in the world but elder sister, Venus, 35, has steadily been recovering her form over the last 18 months after suffering from a debilitating autoimmune disease. Venus was diagnosed with Sjogren’s syndrome in 2011, an autoimmune condition which can cause fatigue and joint pain. Due to the illness her ranking fell to 103 by the end of 2011 before she made her comeback in 2012. She eventually returned to the world’s top 20 in 2014

However, there has been no stopping Serena and the 33-year-old claimed her 20th Grand Slam title at the French Open last month to edge closer to a second ‘Serena Slam’ and her bid to win all four majors in a calendar year.

During a span of eight majors from the US Open in 2001 to Wimbledon in 2003, Serena and Venus Williams participated in Williams vs. Williams Grand Slam finals. There would be two more all-Williams Grand Slam finals, both at Wimbledon, in 2008 and 2009. But since then, they have not met in any round at any Slam. Until now.