The dog starred alongside Witherspoon as Bruiser Woods in the 2001 film. He passed away on Thursday at the age of 18.
"With a sad heart, I have to let all the #LegallyBlonde fans know that Bruiser Woods (also known as Moonie) passed away yesterday," Witherspoon wrote on Instagram.
"He was a sweet little Chihuahua who was very loved. I will never forget all the days we spent together ... I'm sure his tail is wagging in the sky. Sending love to his trainer, the wonderful @tailsticks #RIPBruiser."
He reunited with Witherspoon, 39, in 2010 when she was honoured with a star on the Hollywood Walk of Fame, and during her acceptance speech, "the Walk The Line" star made sure to give her furry friend a special shout out and thank him for attending.
