Serena Williams has added her voice to the numerous athletes and celebrities who have been speaking out and protesting police violence against black people.

Yesterday (Sept. 28), Williams, who is widely regarded as the best athlete in professional sports, penned an emotional post on Facebook after asking her 18 year-old nephew to drive her to a meeting and seeing a cop by the side of the road. All it took was seeing the cop car to incite panic. This is the case for too many Black Americans these days, and Williams was upset that Black people still live with this sad reality in 2016.

"Today I asked my 18 year old nephew (to be clear he's black) to drive me to my meetings so I can work on my phone #safteyfirst. In the distance I saw cop on the side of the road. I quickly checked to see if he was obliging by the speed limit. [Then] I remembered that horrible video of the woman in the car when a cop shot her boyfriend. All of this went through my mind in a matter of seconds."

More than likely, Williams was referring to the police killing of Philando Castile, which was captured by his girlfriend and live-streamed on Facebook before the video was removed. Castile was shot as his girlfriend's four year-old daughter sat in the backseat of the same car.

"I even regretted not driving myself," Williams continued. "I would never forgive myself if something happened to my nephew. He's so innocent. So were all 'the others'," she wrote. 

She went on to say that she knows everyone isn't "bad" but acknowledges that ignorant racists nevertheless affect "millions" of lives. 

"I am a total believer that not 'everyone' is bad It is just the ones that are ignorant, afraid, uneducated, and insensitive that is affecting millions and millions of lives," she wrote. "Why did I have to think about this in 2016? Have we not gone through enough, opened so many doors, impacted billions of lives? But I realized we must stride on- for it's not how far we have come but how much further still we have to go. I [then] wondered than have I spoken up? I had to take a look at me. What about my nephews? What if I have a son and what about my daughters? As Dr. Martin Luther King said 'here comes a time when silence is betrayal.' Won't Be Silent." 

View Williams' post below.