Transcript for Prince William, Prince Harry, Kate and Meghan are the new royal 'fab four': Part 3

Announcer: "20/20" continues with the royal wedding, legacy and love. Reporter: These are the faces of the young Royals who have captured the public's imagination. And are catapulting the monarchy into the 21st century. The future of the royal family will be shaped by what is now known as the fab four, the kind of royal beatles Harry, William, Meghan, and Catherine. And they are seen as authentic stars. They have this energy that makes the royal family attractive, fun, and glamorous. Reporter: A throwback to the 80s when there were four other young Royals. Prince Charles, prince Andrew, and their wives princess Diana and Sarah Ferguson, the duchess of York. When Sarah Ferguson married into the royal family, as suddenly Diana had some partners in crime all in their '20s. Prince Charles, heir to the throne, a good decade older than them all, had to behave. On some levels, we had a fab four, but they weren't particularly functional. Reporter: But it would be Diana and Sarah who would go on to steal the spotlight. Even before Sarah's wedding, the duo would break royal protocol making headlines in the tabloids. They both got dressed up as policewomen and crashed prince Andrew's bachelor party. You're not supposed to do that. Reporter: But both learht. Adjust to life set by palace rules. This was a family that is not like any other family. They have all these rules, all these protocols. They were sort of thrown into the deep end really. Reporter: As Diana stated it during her famous bbc news panorama interview. No, no one sat me down with a piece of paper and said, "This is what is expected of you." We've laughed and smiled and sought each other's advice. Reporter: And being only in their twenties, they sought to inject a bit of fun into their royal duties. When they're at royal ascot which is very proper in the royal enclosure where you're wearing your hats and everything and they're poking friends with their umbrellas. Not the done thing. Reporter: And now a new generation of royal wives with new voices are becoming iconic in their own right and are captivating the world's attention. While William and Harry have been the stars of the show when it came to the younger generation, for a long time, now it's their women who are really the focus of all our attention. Kate, you're Reporter: Kate and Meghan are both 36. The duchess of Cambridge nearly ten years older than Diana at the time of her marriage. Meghan a decade older than Sarah. They had years to become independent women. They definitely have formed and will continue to form a close alliance, because they're in a very unique situation. Catherine has been absolutely -- She's been wonderful. Amazing, as has William as well, you know, fantastic support. This incarnation of the fab four, a lot more functional. You've got four people in their mid-30s. Laser focused on that they want to achieve. Reporter: The four made their first joint Pua sido Christmas day less than a month after the couple's engagement. Meghan's mere presence was history-making. Meghan, who is only just engaged to prince Harry was allowed to attend church, curtsey to the queen in front of the world. The first time we ever saw her do that. Reporter: And she did it in unison with Kate. Meghan already comfortable in front of the cameras has been picking up a few tips as she trades one public life for another. Being a celebrity is something you work for. Being a royal is something you're granted. So, knowing when to stop being a celebrity and start being a princess is critically important. I'd like to imagine Meghan picks her brain, and asks her, you know, "When should I stand here? Who should I let go before me? When do I curtsy?" Reporter: And even for an actress already known for her style, some fashion advice. Kate learned from the queen that you put weights in dresses to make sure that they don't blow up with the wind, and that's something that she will definitely have passed on to Meghan. Reporter: And perhaps all of that advice on protocol is working. Meghan sitting there just like Kate during the fab four's first engagement at the royal foundation. Where they spoke about their hope for the future. We're really looking forward to working as a pair and as a four going forward and hoping to make as much of a difference where we can. Reporter: And even some royal humor when asked do they ever disagree? Oh, yes! The fact that everybody here is laughing means everybody knows exactly what it's like. But you know we're stuck together for the rest of our lives. Togetherness at its finest. Not every family gets along like that anyway. I mean, come on. Even when you're not -- when you don't have all the -- all of the eyes of the world watching. So it's -- it's so lucky that they're all getting along so well. Reporter: And conveniently the four are neighbors. Because they're all based at kensington palace, there will be a lot of interactions that we won't know about. Reporter: William and Kate live in apartment 1a, more like a four-story mansion. And Harry and Meghan just steps away in Nottingham cottage for now, a two-bedroom home. And perhaps soon William and Kate's children could have some new royal playmates. It's been Harry's longtime wish. I can't wait for the day. It'll be fantastic. We know that Meghan wants children. And I think that they will be looking to that pretty soon. Reporter: And it will be important to raise his own children the way his mother raised him. He and his brother talked about this in an itv documentary on the 20th anniversary of Diana's death. As a son, I will say she was the best mum in the world. She smothered us with love, that's for sure. But she understood that there was a real life outside of palace walls. Reporter: As Diana said in that panorama interview -- I want them to have an understanding of people's emotions, people's distress, people's hopes and dreams. If the seed is there, then I hope it will grow because knowledge is power. Reporter: And that seed has, in fact, blossomed into her sons' commitment to bring about change. We've all got that same passion to want to make a difference. I see the future of the royal family as being domestically William and Catherine. In terms of the international perspective, Henry or Harry and Meghan. You have to remember the queen is still figurehead to two billion people. That's a third of the world. She's not doing any long haul travel anymore. That's going on to Meghan and Harry. We're a fantastic team. We know we are, and we'll -- we hope to, you know, over time try and have as much impact for all the things that we care about as much as possible. I am very excited about that.

This transcript has been automatically generated and may not be 100% accurate.