"That '70s Show" had many unforgettable storylines during its run, with moments that ranged from humorous to heartwarming and everything in-between. However, not every storyline reached a logical conclusion, including one from the show's early days that disappeared without a trace.

The plotline in question kicked off in Season 1, Episode 5 when Donna throws a party and we meet her younger sister, Tina, played by actress Amanda Fuller. The episode would be her only appearance, with only a passing mention in Season 2's "Vanstock."

The writers simply determined that Donna should be an only child to make for cleaner storylines. As a result, Tina and Donna's older sister, Valerie (who was only mentioned once and never seen) both ended up going the way of Chuck Cunningham, never to be heard from again.