The summer proved to be a bit like baby boot camp for Prince Harry and Meghan Markle. “The couple often had lunch with Prince William and Kate Middleton,” a royal insider tells Closer Weekly of the months leading up to Harry and Meghan’s pregnancy announcement on Oct. 15.

“William would give Harry tips on fatherhood as they caught up over a beer, while Meghan would play with Princess Charlotte, Prince George, and Prince Louis. They looked at the time they spent with their nephews and niece as good practice!” the insider continued.

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Now with Meghan’s due date coming this spring, Kate, 36, is getting a little antsy — and auntsy — for the newest royal’s arrival. She’s even stepping up her role as mommy coach to Meghan, 37. “Kate’s the one person who understands what Meghan is going through so she’s making it her priority to teach her how to balance her pregnancy with her royal duties in a healthy way,” the insider says. “She’s so excited to show Meghan the ropes. The two have really bonded and they’re closer than ever!”

The fact that Meghan and Harry have been away on their tour of Australia and New Zealand hasn’t put a damper on Kate’s enthusiasm. “Despite Meghan being on the opposite side of the world, she and Kate have been speaking daily,” the insider shares. “Kate was good about checking in and hearing how the pregnancy is coming along. She’s made it her mission to ensure Meghan doesn’t overdo things.”

To that end, Kate’s offered to help with a myriad of details for the baby’s arrival. “Harry and Meghan have two nurseries: one in London and another in the countryside, which Kate is helping to decorate,” the insider reveals. “Meghan has fantastic taste, but she lacks knowledge about day-to-day essentials of baby care so she’s relying on Kate’s expertise. She’s picked out everything from the most soothing crib mobiles to baby toys that George, 5, Charlotte, 3, and Louis, 6 months, all loved.”

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Motherhood, Kate explains, “has been such a rewarding and wonderful experience. However at times it was also a huge challenge — even for me, who had support at home that most mothers do not.” That’s why she’s so sensitive to Meghan’s needs, as Meghan is admittedly nervous about the unknown “and she’s fairly new to London, so she only has a handful of friends in the city,” the insider notes.

Kate is also going all out to throw her sister-in-law a surprise baby shower in early 2019. “She’s a perfectionist, so she’s been prepping for it already,” the insider reveals, “and she’ll invite Meghan’s closest pals from across the pond. Jessica Mulroney, Priyanka Chopra, Serena Williams, and Amal Clooney will all be receiving invites.”

Harry is thrilled to become a first-time dad at 34, calling his niece and nephews “the most amazing things ever. I’ve longed for kids since I was very, very young,” he previously said in an ABC interview, and noted he was just “waiting to find the right person. Someone willing to take on the job.” With Kate’s guidance, his wife more than fits the bill.

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“Meghan’s spent a lot of time at Kate’s looking after George and Charlotte, changing Louis’ diapers, and helping to cook dinner,” the insider reports. The former Suits star “has even put her acting skills to good use, pulling funny faces and speaking in silly voices like a cartoon character. It leaves the children in fits of laughter! Seeing Meghan around her kids, Kate knows for sure that her sister-in-law will be an amazing mom.”

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