Serena Williams penned a letter on Facebook about police violence against minorities on Tuesday, writing that she fears for the safety of her 18-year-old nephew.
In her message, Williams details how she became nervous after seeing a police officer alongside the road as her nephew drove her to an appointment.
Williams's letter comes on the heels of two high–profile police killings of black men. Protests recently broke out after Keith Lamont Scott and Terence Crutcher were fatally shot by police in separate incidents in Charlotte and Tulsa, Okla., respectively. Williams's letter also references the shooting of Philando Castile, whose death in Minnesota at the hands of a police officer was captured on video by his girlfriend.