Her black-and-white snapshot showed the 30-year-old leaning into frame and grinning broadly alongside Katey Sagal, who played her mother, as well as Martin Spanjers and Amy Davdison, who played her younger siblings.
The Charmed actress captioned her photo, 'A little #8simplerules reunion party today with a tiny addition �� @kateylous @martinspanjers @amy_davidson #lennoxsawyerlockwood (someone is smiling down on us)!
Ritter, an icon in the world of American television for his star turn on Three's Company, died in 2003 from a misdiagnosed thoracic aortic aneurysm.
The 54-year-old had been rushed to hospital straight from a rehearsal for 8 Simple Rules For Dating My Teenage Daughter.
The formula begins with each dude's age (for example, 22).
That age is halved (22/2 =11), and 7 is tacked on to the divided result.
"Half, plus seven" is the age-old dating rule for dudes.
Kaley Cuoco, Amy Davidson and Martin Spanjers co-starred as their teenage kids; Bridget, Kerry and Rory Hennessy.
The final series, its title trimmed down to 8 Simple Rules, ended in 2005, having won a cinematography Emmy in 2004.
Ritter was also nominated posthumously in 2004, losing to Kelsey Grammar for Frasier.
The show followed the Hennessy family, centering around John Ritter's fatherly character.
Tragically, John passed away during the show's filming, but his influence clearly lived on in later seasons.