Annie Leibovitz captures loving couple, Queen Elizabeth and Prince Philip

Who's more famous — Queen Elizabeth II or photographer Annie Leibovitz?

It's a toss-up. Let's just say the queen has been famous for longer: She turned 90 in April and now Britain is getting ready to celebrate her official birthday on Saturday at the annual Trooping the Colour parade and pageant.

But pair America's queen of celebrity portrait photography and the British queen — plus, her husband of 68 years, Prince Philip — and you have a boffo combo of fame and success.

No doubt, the media mavens at Buckingham Palace were aware of that when Leibovitz was hired to photograph the queen to mark her 90th — an unprecedented royal birthday. As the longest-serving British monarch (64 years and counting on the throne), the queen is also the oldest monarch ever to reign in the British isles.

Early Friday in London (Thursday evening ET), the palace released the fourth and final Leibovitz photo portrait of the queen, following three other pictures released in April, the month of her actual birthday.

This last photo, taken at Windsor Castle just after Easter, is of the queen with the Duke of Edinburgh, who turns 95 on Friday and who is considered by historians and royal watchers the key to her success as a monarch. Together, they make up the longest-married (69 years in November) monarch-and-consort in British history.

Like the earlier photos, this one, too, displayed Leibovitz' widely-acclaimed lush style combined with her empathetic insight. The earlier photos featured the queen at Windsor Castle, with her beloved dogs, with her great-grandchildren and youngest grandchildren, and with her only daughter, Princess Anne the Princess Royal.

The latter picture captured the warmth of the relationship between mother and daughter, something not usually on display, so it was a new glimpse for the British of two people they are used to seeing in different circumstances. The picture of the queen surrounded by the youngest and cutest of her many descendants had the look and patina of an Old Master painting, but with a sense of humor.

Philip's 95th birthday is yet another record, but he generally prefers to keep his own celebration low-key so as not to interfere with the queen's official birthday hoopla. But no doubt it will be mentioned at the annual Service of Thanksgiving at St Paul's Cathedral on Friday.

Meanwhile, central London is already dripping with bunting and Union Jacks all the way down The Mall and above Regent Street and Oxford Street in advance of the queen's birthday celebrations on Saturday.

Most of the royal family, including great-grandson and future king Prince George, are expected to turn out, as is traditional, for the colorful Trooping pageantry; later, they will join the queen on the balcony of Buckingham Palace to watch the usual flypast of RAF jets.

On Sunday, the queen, Prince Philip, Prince William and Duchess Kate and Prince Harry will join an expected 10,000 representatives of charities and other organizations for the Patron’s Lunch, a picnic on The Mall organized by the queen’s eldest grandson, Peter Phillips.

It's expected to rain, naturally. But guests will be issued both a plastic rain poncho and sunscreen cream just in case.