Rob Lowe is mourning the loss of his dog.

The 52-year-old actor took to Instagram earlier this week to share that his family's Jack Russell Terrier sadly died after 16 years.

"Buster was the best #dog a family could ever ask for. An unforgettable spirit of love, loyalty and energy. And a huge part of raising our sons. We are grateful to have had him for so many years and so many memories. No one will ever forget our great #Buzzoom," The West Wing star captioned the snapshot of his furry friend looking healthy and happy prior to his passing.

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Our thoughts are with Rob, his wife, Sheryl Berkoff, and his sons Matthew and John Owen during this difficult time.