Transcript for Surprise! Proud parents get a bit of the royal treatment

Finally tonight, the world waiting for William and Kate when out walked this couple. We've seen that doorway to St. Mary's before, June 21st, 1982. Princess Diana and prince Charles with a newborn prince. Two years later, the second prince, Harry had been born. 34 years later, the newest member of the royal family in duchess Catherine's arms. Five years ago, prince George. Then, princess Charlotte. That doorway made famous by the Royals. But today, there was also this couple. Cameras from all over the world waiting for William and Kate, when this couple emerged before them. No one knew them, but the cameras snapping the photos just in case, then, their closeup. Then, that new dad capturing a shot on the photographers. A congratulations from the crowd. Congratulations! Thank you! Reporter: And then a thank you from the other couple, too. They deserve their moment, too. Thanks for watching. I'm David Muir. I hope to see (Leader) So, how many of them

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