Kate Middleton received a welcome typically reserved for competitors when she descended the steps at Wimbledon to her front-row seat in the Royal Box on July 14, and she was visibly moved by the standing ovation.

For the Princess of Wales, 42, who shared in June that she experiences “good days and bad days” as she continues treatment for an undisclosed form of cancer diagnosed earlier this year, this was clearly a good day. She and daughter Princess Charlotte traded giggles and chit-chat alongside sister Pippa Middleton, and — despite being front and center for around two hours and 40 minutes — she appeared to have gained some comfort from the reception and being out and about.

“This will have given her sustenance. She has gone through something awful and stressful, and it is crucial to have little wins to look forward to or to give you the courage and energy to go forward,” a palace insider tells PEOPLE exclusively in this week’s issue. “And this was it.”

The rare outing (announced the day before and just her second public appearance of the year) didn’t come without much thought, planning and steely preparation on the royal’s part.

“It showed a lot of courage and character, as she knew that the world was watching,” says Robert Jobson, author of the new book Catherine, the Princess of Wales: A Biography of the Future Queen, out Aug. 6.

Princess Kate attended the last day of the Wimbledon championships in her role as patron of the All England Lawn Tennis and Croquet Club.

Photographer Karwai Tang captured her memorable entrance, made even more special by Princess Charlotte’s look of admiration toward her mother.

“She usually comes in, walks down and into her seat,” Tang tells PEOPLE. “But she stood for a while and took it all in. For her to acknowledge it and take in the applause was special. Wimbledon had been waiting with bated breath for her to return, and she was back.”

Since her last high-profile outing alongside the royal family on June 15 at Trooping the Colour, the Princess of Wales has been focusing on her recovery and finding joy in her children, Prince George, 10, Princess Charlotte, 9, and Prince Louis, 6, while gradually returning to her duties behind the scenes. A palace source confirms that Princess Kate has been making calls, speaking with staff and staying informed on the latest research for her royal causes while doing “a little work from home,” as Kate described on June 14.

Adds a source close to the royal household: “It’s good not to feel under pressure and just take her time and have slow days if she needs to.”

That shift in priorities around her health has been crucial.

“Before, she used to live her life by the calendar, and now she is living her life, and the calendar comes in after,” Jobson says. “She will be back, but when you have had an experience like this, it changes your perspective and the order of things.”