See Camilla’s New Birthday Portrait – by One of Princess Diana’s Favorite Photographers

Camilla, Duchess of Cornwall turns 70 on Monday — and she is being celebrated with an official new portrait.

The image was taken by famed photographer Mario Testino, who famously captured Princess Diana in her last official photo shoot. (Those photos are currently on exhibit at Diana's childhood home, Althorp.)

In the new photograph, Camilla — in a navy blue dress coat by designer Fiona Clare – poses with husband Prince Charles in the Morning Room at Clarence House, their London residence.

It's the second time Testino has publicly photographed Camilla. In a statement, the photographer said he was "honored" to capture the couple "on this very important date," noting that after he first photographed her in 2006 he "discovered a kind and beautiful person with a wonderful sense of humor. Doing this latest assignment to celebrate Her Royal Highness's 70th birthday is a true honor."

Camilla turns 70 on Monday, but has already been the guest of honor at a party at home at Highgrove house, near Tetbury, Gloucestershire on Saturday evening.

In fact, she has been doing a lot of merry-making of late: Last week birthday wishes were displayed on a red London bus as she hosted a party for schoolchildren to promote a literacy campaign. On Thursday, she and Charles welcomed charity friends to mark Camilla's contribution to the world of royal duty — something she didn't start until marrying Charles in 2005 at age 57.

She is also the subject of a semi-authorized new biography by author Penny Junor, The Duchess, in which those close to her tell her side of the story in detail for the first time.

"Clearly when people meet her she has that je ne sais quo," a source in royal circles told PEOPLE last month. "She does have that magic spell that draws people in." Adds Christopher Wilson, author of the 1994 biography A Greater Love: "What she had was chutzpah."

Junor's book also brought back stories about the affair that rocked the British royal family just as friends and family of the late Princess Diana are set to mark the 20th anniversary of her death in August.

Source: See Camilla's New Birthday Portrait – by One of Princess Diana's Favorite Photographers