Queen Elizabeth II was only person eligible to be monarch because her father had no male children.
This birth marks the first time in almost 120 years that a reigning monarch, Queen Elizabeth II, 87, is alive at the same time as three generations of heirs: Prince Charles, 64, Prince William, 31, and, now, the latest addition to the family.
The baby boy will someday be the monarch of 16 sovereign states and commander of the British Army, among having other royal responsibilities.
"This new baby physically represents the mixture of history and new blood coming in, and the promise," Lacey said.
The roller-coaster-like relationship between the public and the royal family is at a high point right now, thanks, in great part, to Middleton and her grounded nature, Lacey said.
"You have to strike a balance between the dignities and traditions of the family and the monarchy with something new, and she's got that something new," Lacey said. "I think it's freshness, it's energy, it's directness, it's honesty. It's coming from a hardworking family which, to use an English expression, pulled itself up by its bootstraps."
The royal couple announced the pregnancy Dec. 3, 2012, when the Duchess, 31, was admitted to King Edward VII Hospital in central London with hyperemesis gravidarum, an acute morning sickness that requires supplementary hydration and nutrients.
Royal babies have typically been born within a year of marriage. Princess Diana gave birth to William 11 months after her wedding and the queen gave birth to Prince Charles six days before her first wedding anniversary.
Prince William and Kate were married April 29, 2011.
"I think this is something they've had in their minds that they really wanted to do and they're so excited that it's happening," Murphy said. "They've got friends who have kids, they're at a really great age, they've been together for a long time, they're still young enough to have lots of energy. I think both of them are just really, really excited about becoming parents."
It is widely expected that the new parents will strive for normalcy in their child's life, much like the prince's late mother, Princess Diana, instilled in her two sons, William and Harry. Diana famously made it a point of taking her boys beyond the palace walls for outings to the movies, amusement parks and McDonald's.
She also involved them in her charity work and famously took her young sons on a visit to a homeless shelter in 1996, the year before she died in a car accident. William is still involved with the shelter.
"She played a huge part in my life and Harry's growing up in how we saw things and how we experienced things," Prince William told ABC News last year of his mother. "She very much wanted to get us to see the role in this of real life and I can't thank her enough for that because reality bites in a big way and it was one of the biggest lessons I learned, is just how lucky and privileged how many of us are."
Such an attitude will likely influence the way William and Kate raise their new baby and future ruler.
"The baby is going to be a different sort of leader of the country in that the whole essence of the royal family nowadays succeeds or fails on its ability to communicate with the rest of the population," Lacey said.
"We're not looking for inspired, divine leadership. We're looking for common sense and humanity," Lacey said
"I think that will be the priority for the parents, to give the child the most normal possible upbringing not only for its own good, but for the good of the job it's got to do in the future. It's got to have the common touch."