Though Kensington Palace may look more like a series of townhouse apartments than a palace, it was perhaps Diana's one safe haven: the place where she lived and raised her children.
And it is here that William and Kate will raise theirs. Diana paved the way for a new kind of royal parenting, setting a standard for mothering a future monarch.
Prince William has said he wants to spare his wife the inevitable comparisons to his mother. But in many ways, Diana has been part of this pregnancy from the very beginning.
The world waited two years for Duchess Kate's announcement, but Diana was pregnant just three months after her wedding. From the beginning, she rebelled against the royal traditions of arm's-length parenting.
Prince William was the first heir to the throne to be born outside palace walls, in a hospital. This was followed closely by another royal first.
"Diana is largely reported to be the very first mother within the royal family to breastfeed," said ABC News royal correspondent Victoria Arbiter. "Of course, that's hard for us to know for certain, but Queen Victoria was adamant that she found breastfeeding disgusting. She thought babies were ugly, and she didn't really enjoy any part of being pregnant, yet she had nine children."
Because of Diana, that taboo has been removed for Kate and the new baby.
"I'm sure she'll do exactly what most women in this country do," said Daisy Goodwin, author of "My Last Duchess." "Which is to breastfeed for two or three months. And then, you know, get some stuff and give them a bottle."
Princess Diana broke with the royal tradition of spending months touring the Commonwealth without the kids. She insisted on including nine-month-old William on an official visit to Australia.
"And [people] were like, 'Breaking royal precedent,'" Goodwin said. "But it was brilliant, because ... we all really warmed to her. Because no woman wants to leave her baby, and that was what made Diana so lovable -- that she always absolutely adored her children."
Judy Wade, royal contributor to Hello! magazine, said she used to call Diana a "rebel royal mum" because of Diana's breaks with tradition.
"Sources within Kensington Palace would say to me, 'Every morning the boys would run in their pajamas into her bedroom, and she'd have her arms open wide to hug them.'"
At Diana's insistence, William became the first heir to the throne to attend public school. His personal bodyguard, Ken Wharfe, was with him on his first day.
"Diana said to him in the car, 'Now listen, William, there's going to be a lot of photographers at your new school, so you need to behave yourself.' And he, in this sort of just William way, said to his mother, just below the pink cap, 'I don't like 'tographers,'" Wharfe said.
"She said, 'Well, you're going to get this for the rest of your life,'" Wharfe said.
Arthur Edwards, royal photographer, has been photographing William since he was born.
"William hated the press," Edwards said. "He didn't like the whole idea of being photographed all the time. He just didn't accept it."
Still, Princess Diana wanted to give her sons a normal life.
For centuries, young royals grew up separately from their subjects. When Queen Elizabeth II was young, Arbiter said, the palace had to bring a Girl Guide company into Buckingham Palace so that she had children her own age to socialize with.
"I think that really is the long-lasting legacy that Diana has left William and Harry," Arbiter said. "She took them outside the palace walls."
Patrick Jephson, Princess Diana's chief of staff for six years, met William when the prince was six years old.
"She made sure that they experienced things like going to the cinema, queuing up to buy a McDonalds, going to amusement parks, those sorts of things that were experiences that they could share with their friends," Jephson said.
Diana had to balance the clash between these normal experiences and the fact that her sons' lives would in many ways be anything but normal.
"It was a very difficult dilemma for Diana to prepare them for the very distinctive, unique life that they have had to lead," Jephson said. "And she did it very cleverly, I think."
For example, he said, Diana took them to hospitals and homeless shelters to introduce them to the work she had found so fulfilling in her own public life -- and that would be their destiny.
Wharfe recalled her taking seven-year-old William to a homeless center.
"This was done completely out of sight of any camera or media. This was Diana's way of actually saying to William, 'Listen, it isn't all what you think it is living at Kensington Palace.' That was a quite a brave thing on Diana's part."
As adults, both William and Kate have followed in Diana's footsteps. Last year alone, Kate made 111 appearances, many in support of charitable causes. William still actively supports Centre Point, the homeless shelter he first visited with his mother. Last year, William spent the night on the streets of London to highlight the plight of the homeless.
"She played a huge part in my life and Harry's growing up, in how we saw things and how we experienced things," William said in a 2012 interview with ABC News' Katie Couric.
"She very much wanted to get us to see the rawness of real life. And I can't thank her enough for that, 'cause reality bites in a big way, and it was one of the biggest lessons I learned is, just how lucky and privileged so many of us are -- particularly myself," William said.
Diana also showed by example how to handle encounters with the public, beginning with William's first official public outing, at 10 years old.
"Even as an adult that might have been quite intimidating," Jephson said. "But William squared his shoulders, he went and did his duty, he did his job, and he made sure that everybody who met him that day had a memory to treasure forever."
"Diana said to William, It only may be 10 seconds out of your life, [but] it could be years of happy memories for the person you meet," Jephson went on. "And that sense of respect for people in the crowd is something that I think we can see Diana has passed on very successfully to her children."
William told Couric, "She really minded about who she met and how she did the engagements. And she wanted to give everyone a certain amount of time so that they felt they were actually engaging with her. And I thought that was a very good learning point for me."
Diana had a common touch that made her loved, particularly by children. She always crouched to talk personally -- eye to eye.
"Diana was the first member of the royal family to do this," said Ingrid Seward, editor of Majesty magazine. "The royal family used to say that everyone had to be deferential to them. But Diana said, 'If someone might be nervous of you or you're speaking to a very young child or a sick person, get yourself on their level."
Footage of Kate's public appearances shows that she has internalized this lesson.
"When you see Kate kneeling to talk to someone, it is very reminiscent of Diana -- throughout her life," Seward said.
Diana's death, from a car accident while her car was being chased by paparazzi, renewed William's childhood distrust of the media.
"William absolutely loathes the media," Seward said. "He is adamant that they are just scum. And you absolutely can't blame him. I mean, in his mind, and in Harry's mind, the media were the ones that killed his mum."
The tragedy provided a final lesson from Diana: Beware the paparazzi.
Last year, two French tabloids published topless photos of Kate. In his own departure from royal ways, William became the first senior member of the royal family to sue in a foreign court.
The case is ongoing, but William's message is clear: Respect the privacy of Duchess Kate and their soon-to-be-born child. Diana would be proud.