Animal Fair Media / Getty Images North America 1 / 5
Animal Fair Media / Getty Images North America 1 / 5

RIP, Jackie.

Serena Williams took to Instagram on Nov. 24 to post a heartfelt tribute to her dog, Jackie. The pup, a 16-year-old Jack Russell Terrier, tragically passed away from old age, and Serena wrote about the heartbreaking experience on social media.

"Today really is hard for me. My special friend in which I got at 17 (2 weeks before I won my very first Grand Slam) left me today," Serena shared of her longtime companion. "She was 16 years young and up until a few days ago was still sprinting. Her poor body gave out this morning and she had a way of telling me it was time for me to be brave and let her go."

Jackie had been in Serena's life since 1999. Fortunately, she had her father by her side as the two said goodbye to their four-legged family member. Fans of the tennis superstar were well acquainted with Jackie, who Serena often posed with in photographs.

The coming weeks will no doubt be difficult for Serena, who concluded her tribute with a sad realization about Jackie truly being gone, and a reminder to those with pets to cherish them.

"I got out of the shower this afternoon and she was not there to lick my leg as she always did everyday to remind me how much she loved me. I feel so lucky to have such a special friend. Give your dog, cat, pet a big hug. #breakingheart #bff Jackie Baila Pete Williams I will miss you and your memory will live forever."

Serena also posted an Instagram collage of Jackie alongside her furry siblings, the tennis champ's other pups, Lauralei and Chip, ending the caption with, "thank you for the kindness and joy you brought us."