"It was thrilling. it's an amazing experience to be part of history and a rare honor," Anderson tells PEOPLE. "There's been a lot of calm excitement in the palace all day since the announcement that she was in hospital and people were just waiting for the good news."
Anderson, 44, is Queen Elizabeth's press secretary, tasked with making the final journey with the anxiously awaited birth notice (handed off by Prince William and Kate's press secretary Ed Perkins) and fix it on the easel for Her Majesty's subjects (and the rest of the world) to see.
Her appearance, holding a gilded frame and accompanied by a formally-coated man, was met by cheers from the hundreds pressed against the gates. "Three cheers for Kate and William and the little Prince," called out a voice. "Hip hip hurrah," the crowd answered three times.
Cindy Eve, 58, of Richmond, said she led the cheer because she is delighted for Prince William. "I get emotional," she said in a choked voice. "Because of losing his mum, but now he has his own little family."
The electric energy stayed in the air late into the evening, as crowds filtered through for their turn to see the easel, which held the proclamation stating a son was born safely at 4:24 p.m. and "Her Royal Highness and her child are both doing well." Random singalongs of "Happy Birthday to you, Royal Baby" could be heard.
"I just want a cup of tea now," says Anderson "in my 'It's a boy' mug."
A Popular but Feisty OfficialAnderson, a tall, slender mother-of-two (she's married to a former naval officer who now works in London's financial district), is one of three key women around the Queen. Along with assistant private secretary Samantha Cohen and dressmaker Angela Kelly, she is part of the 87-year-old monarch's team advising her every day.
Anderson joined the palace, as an assistant press secretary, in 2001 coming from a public relations post in the U.K. government where she worked in the Cabinet Office, aiding Margaret Beckett, a senior member of the then-Labour administration, and was made press secretary to the Queen when Cohen was promoted in 2007.
"She is a smart woman – smart and sassy," says experienced royals correspondent Judy Wade.
Courtesy Jim Roberts
Living in the home counties just northwest of London, she likes to shop for clothes at the designer outlet stores at Bicester Villlage (where Kate has been known to visit) and has a nose for a good deal. "She's great at sussing out the good bargains in sales," says a friend.
It's a thriftiness that would gain her praise from her boss, whose role at the pinnacle of public life in Britain is passionately supported by her press spokeswoman.
When she got her first post in the press office at Buckingham Palace, Anderson said it was a "dream job come true."
Now, she's living it every day.