And she did it in perfect, princess-to-be style.
On a bitterly cold London evening, Middleton, 28, attended the annual Christmas carol concert to benefit a charity dear to her fiancé's heart, the Henry van Straubenzee Memorial Fund. (Her betrothed, meanwhile, was in Switzerland with David Beckham in the hopes of landing Britain a bid to host the World Cup in 2018.)
In 2009, William, 28, became a patron of the memorial fund, which helps set up schools in Uganda. It also happens to be the only philanthropy in which he and his brother, Prince Harry, are jointly involved. The charity is named for a young classmate of the princes who died in a car crash.
At the event on Wednesday night, a royal protection officer driving a Range Rover dropped Middleton off at the door of St. Luke's Church in Chelsea, thwarting efforts by photographers to get a clear shot of the royal fiancée.
By the end of the evening, she was seen enjoying the company – and attention – of many of the couple's friends in the foyer of the church, several of whom had not seen her since the big announcement. Members of the royal household and a friend accompanied Middleton as well, according to observers.
She was one of the last to leave, after chatting in the foyer of the church for more than an hour after the service. A fellow guest tells PEOPLE, "She was on top form. She looked radiant and was charming everyone."
Wearing a black overcoat, she then dashed out through a flurry of snowflakes to the waiting four-wheel drive SUV.
"It's incredible how things have changed," one witness tells PEOPLE. "Last year she left [this event] in a taxi. This time she had a press officer and a specially-protected Range Rover."