Willow had an illness which was "cancer related" and it's reported that The Queen made the hard decision to have her companion put to sleep so that the almost 15-year-old dog would not suffer.
"Whisper was a friendly chap and followed her everywhere", a source told the news outlet.
The Queen has been surrounded by corgis since she was a teenager. This leaves the queen with two dogs known as "Dorgis".
The dog, Whisper, was not a descendant of the queen's original corgi, but rather the pet of a former gamekeeper, Bill Fenwick. "The Queen thought it was a bit obscure and preferred the proper spelling".
Queen Elizabeth's last corgi has passed away.
Her offer to take in Whisper was seen as returning the favour.
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Her Majesty's corgi breeding fascination began during her teenage years when she was given a Welsh Corgi, named Susan, by her father George VI.
Vets were called in last week while the Queen was at Windsor Castle after the wedding of her granddaughter Princess Eugenie.
Buckingham Palace refused to comment.
The pair reportedly grew very close in the last two years and sources said the Queen is "deeply saddened" by the loss, according to The Daily Mail.
Bill's wife Nancy died three years ago and according to reports, she used to look after the Queen's dogs.
The Queen loves her corgis! It is probably because Willow was the last link to her parents and a pastime that goes back to her own childhood.