Credit: IMDB; Getty Images Photo: Phylicia Rashad: Clair Huxtable

If you're a fan of Grey's Anatomy and/or So You Think You Can Dance, you are obviously a fan of actress/choreographer Debbie Allen, who plays Catherine Avery on the former and sits in on the judging panel on the latter. But you may be surprised to learn that the three-time Emmy winner is the younger sister of a TV actress who's perhaps even more famous.

Who? That's exactly what we asked Viggle LIVE! users during the March 21 episode of Grey's Anatomy — in which Catherine roared back into Seattle to take her son, Jackson, to task for marrying April on a whim.

But you guys weren't daunted! A whopping 74 percent of you nailed the answer. Debbie's older sis is Phylicia Rashad, aka the actress who played Bill Cosby's wife for 16 years over the span of two different sitcoms: The Cosby Show and Cosby.

Try your hand at the trivia! Download the free Viggle app now.

Phylicia and Debbie are two of four children of artist Vivian Ayers and orthodontist Andrew Allen — Phylicia was born in 1948 and Debbie in 1950.

Meanwhile, 16 percent of you guessed Diahann Carroll — the first black person to receive an Emmy nomination for her role in Julia — and the actress who played Burke's mom on Grey's! And 10 percent thought it was Nichelle Nichols, aka Uhura in the original Star Trek series.

Wanna impress us with your TV and movie knowledge? It’s easy — and you even get to earn rewards for watching your favorite shows. All you have to do is download the Viggle app, get watching, and join in on the fun!

Dan Clarendon is an assistant editor at Wetpaint Entertainment. Follow him on Twitter and Google+!