New portrait of Queen Elizabeth and Prince Charles released

Britain's Queen Elizabeth has been celebrating her 90th birthday year in 2016. Photo / AP

A photograph of the Queen and Prince Charles has been released to mark the end of the monarch's 90th birthday year.

The previously unseen picture, taken by fashion photographer Nick Knight in May, shows the mother and son in the White Drawing Room at Windsor Castle before the final night of the Queen's celebrations at the Royal Windsor Horse Show.

First look: As a year of 90th birthday celebrations draw to a close, we would like to share this special photo of The Prince and The Queen. pic.twitter.com/0qfB41c5VG

— The Prince of Wales and The Duchess of Cornwall (@ClarenceHouse) December 17, 2016

Charles, wearing a black dinner jacket, appears to be smiling at the Queen - dressed in a sea green and dove grey brocade dress by Angela Kelly - who is looking directly ahead.

The Queen turned 90 in April and marked the milestone with a series of events - including a private black tie banquet at Windsor Castle with her friends and loved ones.

In June, she celebrated her official birthday with a service of thanksgiving and a picnic on The Mall for 10,000 revellers.

"I wanted to create a modern portrait that showed warmth and humanity as well as strength and tradition," Kniight said.

- AAP