Princess Charlotte, Prince George in New Photos for Queen's 90th Birthday

— -- New photos released on the occasion of Queen Elizabeth II’s 90th birthday show the queen with her two youngest grandchildren and great-grandchildren, including Prince George and Princess Charlotte.

The three photos were taken at Windsor Castle just after Easter by famed photographer Annie Leibovitz.

Leibovitz captured Her Majesty in the castle’s Green Drawing Room holding, in the tradition of the royal portrait, her youngest great-grandchild, 11-month-old Princess Charlotte.

Charlotte’s older brother, 2-year-old Prince George, is also featured in the photo, along with more of the royal family’s youngest members, including Mia Tindall, the 2-year-old daughter of Zara and Mike Tindall; James, Viscount Severn, 8, and Lady Louise, 12, the children of the Earl and Countess of Wessex; Savannah, 5, and Isla Phillips, 3, the daughters of the queen’s eldest grandson, Peter Phillips and his wife, Autumn.

Including the younger members of the royal family in the commemorative photo was reportedly a decision made by the queen, who thought it important to reflect on the importance of family.

In the photo, Prince George is wearing burgundy shorts with a $35 sweater by Spanish children’s wear designer Fina Ejerique. Princess Charlotte’s $30 dollar dress from Spanish brand m&h was a gift from the family’s nanny Maria Borrallo.

George, who calls his great-grandmother “Gan Gan,” appears to be thrilled to be at her side. In a spontaneous moment during the photo shoot, young Mia Tindall picked up the queen’s iconic handbag which she is known to carry everywhere.

A second photo by Leibovitz shows Her Majesty among Windsor Castle’s private grounds with four of her beloved pet dogs.

The third and final photo taken by Leibovitz shows the queen in Windsor Castle’s White Dining Room with her daughter, the Princess Royal.

In addition to the newly released photographs, the royal family will mark the queen’s special occasion Thursday with a walkabout in Windsor to celebrate her 90th birthday.

The Queen, Prince Philip and the Prince of Wales and Duchess of Cornwall will attend a ceremony Thursday in which 1,000 beacons will be lit around the U.K.

Prince Charles will also host a birthday dinner for 60 family members and close friends of Her Majesty in the Waterloo Chamber of Windsor Castle.

Prince William revealed to Sky News that he and his younger brother, Prince Harry, have decided to give their grandmother a joint present.

“What do you give the queen? That’s like the hardest question ever so we regularly have a lot of debates,” William said. “Harry and I have decided to have a joint present this year and it makes it a bit easier when we can share the responsibility of getting it right.”

William also revealed the queen’s relationship with the royal family's youngest members, including his own two children.

“She’s always been incredibly loving towards the children and I’ve seen her now with Charlotte and George,” he said. “She's very doting on the children, and particularly Charlotte. She's fascinated by what Charlotte gets up to."

A set of 10 new stamps were also released to mark the queen’s 90th birthday.

Four generations of the Windsor family -- the queen, Prince Charles, Prince William and Prince George -- are the centerpiece of the 10 stamps. The remaining six stamps each depict a moment in Her Majesty’s life and work.