Queen Elizabeth celebrates 96th birthday in milestone jubilee year

Queen Elizabeth pictured with her fell ponies, named Bybeck Nightingale (right) and Bybeck Katie.

Britain's Queen Elizabeth II celebrated her 96th birthday on Thursday, in the same year that marks her 70 years on the throne.

The Queen has traveled to Sandringham, her estate in Norfolk, eastern England, for a private break, Buckingham Palace told CNN.

A portrait released to mark the occasion shows the monarch standing between two fell ponies named Bybeck Nightingale and Bybeck Katie.

The photo was taken in the grounds of Windsor Castle in March, according to the royal family Twitter account.

William and Catherine, the Duke and Duchess of Cambridge, sent the Queen a birthday message on social media.

"Wishing Her Majesty The Queen a very happy 96th birthday today!" reads the tweet.

"An inspiration to so many across the UK, the Commonwealth and the world, it's particularly special to be celebrating in this #PlatinumJubilee year."