Transcript for Prince Philip will be at Prince Harry and Meghan Markle's wedding: Palace

We turn to the story in Windsor. We're about 25 miles from London at Windsor castle where Meghan Markle will marry prince Harry. Prince Charles will walk Meghan down the aisle and the interview with princess Diana. James Longman here tonight. Reporter: Tomorrow, her life will change forever. Before she joins a new family, Meghan Markle will spend the night at this hotel with her mother, Doria Ragland. How are you feeling miss Markle? Wonderful, thank you. Reporter: The bride-to-be looking radiant and calm, after a family tea with her mother, her fiance, the queen and prince Phillip. The town of Windsor officially "Harry and Meghan central." The streets packed with royal well-wishers, straining for a glimpse of Harry and William. Look at the excitement. People can't wait to meet prince Harry and his brother. There he is. Reporter: The princes making their way through town. Harry relaxed. Shaking hands and taking in the moment. William, Harry! William, Harry! Reporter: And tonight, as they get the finishing touches ready, we're learning more details about the walk down the aisle. With Meghan's father unable to attend, she's asked her new father-in-law prince Charles to step in. The wedding, at St. George's chapel on the grounds of Windsor castle. Meghan will enter up these stairs, with her bridesmaids and pageboys, including prince George and princess Charlotte. She will proceed down the aisle and meet prince Charles here. And he will walk her up to the altar to marry her prince. Harry embraced by his mother all those years ago was asked what princess Diana would have thought about this American princess. They would be thick as thieves. She would be so excited. Reporter: His mother once asked what she wanted for her boy. If you find someone you love in life, you've must hang on to it. Reporter: Now her youngest prince set to marry. You know it is days like -- days like today when -- when I really miss having her around and miss being able to share the happy news. But you know with the ring and with everything else that's going on I'm sure she's -- She's with us. I'm sure she's with us, yeah. James Longman with us tonight. Prince Harry said his mother would have loved Meghan Markle. Princess Diana's sister is speaking tomorrow. Yes, she will be representing Diana's family at the wedding. Both prince Charles and princess Diana looming large. Thanks James. I hope and me for a special "20/20." Then first thing in the morning set your DVRs and wake up with robin and me. History in the making. Get your coffee. It's early. There's much more ahead on "ABC world news tonight."

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