Tennis legend Serena Williams shared an unsettling Facebook post on Tuesday about the sad reason she regretted asking her nephew to drive her to work meetings, alluding to recent police killings of black men.

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Williams opened her post by saying that she recently tasked her 18-year-old nephew with driving her to meetings so she can work in the car. She wrote that she "regretted" asking him to be her chauffeur today, as she saw a police officer on the road and started to panic. Suddenly she feared that she may have put her nephew in danger, given the many recent police shootings of black men.

In her post, Williams alluded to the recent death of Philando Castile, a black man who was fatally shot by a police officer with his girlfriend Diamond Reynolds in the car; Reynolds lived streamed the aftermath of the shooting on Facebook Live.

"In the distance I saw [a] cop on the side of the road," Williams wrote. "I quickly checked to see if he was obliging by the speed limit. Than 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. I even regretted not driving myself. I would never forgive myself if something happened to my nephew. He's so innocent. So were all 'the others.'"

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Williams added that it's a shame she has to worry about something as simple as asking her nephew to drive her in 2016:

"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."

Williams' post has been shared nearly 8,000 times as of writing this article:

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Williams' post comes a week after the death of Keith Scott, a black man who was fatally shot by authorities in Charlotte. Scott's death sparked protests in the city and also pressured officials into releasing this footage.