As the queen hits 90, we hear about the 2 sides of "Lilibeth"

Britain honors Queen Elizabeth on 90th birthd... 03:48

WINDSOR, England-- Britain wishedQueen Elizabeth II a happy birthday on Thursday with music, ceremony and personal greetings.

As CBS News correspondent Mark Phillips reports, if any proof were needed that queens are different from you and me -- it's in their birthdays; queens get two of them. There's the real one, which for Queen Elizabeth II is Thursday. Then there's an official one, with full state trappings, in June.

But even for queens, it's the date on which one was born that counts.

A choir sang "Return to Sender" as the queen began her birthday celebrations Wednesday with a visit to a post office west of London.

Elvis may be the king of rock'n'roll, but Phillips says the British monarchy most certainly hasn't left the building, and new stamps issued for the queen's 90th indicate it'll be around for a while yet. A new family portrait shows the queen, and three kings in waiting.

Elizabeth II becomes Britain's longest-reigni... 05:18

According to the second-in-line, her grandson Prince William, Queen Elizabeth has been the best possible teacher.

"I think the queen's duty and her service, her tolerance, her commitment to others -- I think that's all been incredibly important to me and it's been a real guiding example of just what a good monarch could be," William said.

She's a 90-year-old monarch who's been on the throne for 64 years. Maybe that's why the next choir sang "When I'm Sixty-Four."

This queen has witnessed so many milestones over her long life, a collection of 90 photographs taken over 90 years has been pulled together in celebration.

But this is a private milestone too, and the latest photo of the queen with her youngest grandchildren and her great-grandchildren may be the most personal, with 11-month-old Princess Charlotte in her arms, and William and Kate's other child, Prince George, in short pants just beside her.

People who know her say there are two queens; the public, dutiful one, and the private one -- a country girl at heart, where she can be herself.

No one knows that better than her cousin Margaret Rhodes, who's known the queen since childhood and who still enjoys a private friendship with her.

"I call her by her childish name. She's Lilibeth," Rhodes said.

"Does she still respond to Lilibeth?" Phillips asked.

"Oh, yes," Rhodes said.

Lilibeth -- even at 90 -- is showing few signs of slowing down. Other members of her family now fill in at some official engagements, but she still does plenty of them herself. Being there is what the job is all about.

"Wev'e had prime ministers by the dozen, but we have the queen who is always there, you know? And I think that gives people a sense of safety somehow, almost, you know," Rhodes said. "I think that she herself... does all the things that she's proud to do like putting on a crown and opening Parliament and things like that, but at the same time she likes to take her dogs for a walk, talks to the ponies, and pull out weeds she sees. She's a mixture."