According to British media reports, Willow was put down at Windsor Castle after battling cancer.
Willow, 14, was the last of a group of purebred corgis descended from Susan, a corgi that then-Princess Elizabeth received as a gift, ABC News reported. Willow was featured in Queen Elizabeth's 90th birthday photos taken by Annie Leibovitz in 2016 and has appeared alongside Queen Elizabeth during numerous public appearances over the years.
Queen Elizabeth, 91, is believed to have raised dozens of corgis during her life. She still has a dachshund-corgi crossbreed and another adopted corgi not descended from Susan.