The end of an era.
The dog had cancer, and the Queen didn't want her favorite pet was suffering then.
Queen Elizabeth II's love of corgi dogs is legendary.
Hoey says the corgis were so pampered the Queen even hires a homeopath to treat them whenever they are ill.
The queen still has two dogs romping around the grounds of her palaces, however.
However, the Queen still has two corgi-dashshund crosses named Vulcan and Candy and previous year, she is said to have adopted another corgi named Whisper, following the death of hiss owner who was a Sandringham gamekeeper.
Meanwhile, Willow had featured in the Olympics opening ceremony sketch along with James Bond's Daniel Craig and the Queen alongside with corgi named Holly, who died in 2016 at the age of 13.
The Queen has had more than 30 dogs originating from Susan's puppies Sugar and Honey, who were born in 1949.
Former royal butler Paul Burrell, whose duties included being armed with blotting paper and a soda syphon to mop up doggy accidents, claimed he was once knocked unconscious after nine corgis tripped him up.
Willow was the 14th generation descended from Susan, a corgi gifted to the then Princess Elizabeth on her 18th birthday in 1944.
A source told the Daily Mail newspaper: "She has mourned every one of her corgis over the years, but she has been more upset about Willow's death than any of them".
Ever since the Queen was a young girl, the breeding and care of corgis has been a significant part of her life; indeed, she herself has said, "My corgis are family".
When at Buckingham Palace, the dogs slept in raised wicker baskets in a room near the royal apartments, where they roamed freely.