Calling their bond "togetherness at its finest", the 36-year-old mum-of-three has been Meghan's rock during the pregnancy.
According to Life & Style, Meghan's been turning to Kate for all kinds of baby advice.
"It'll mean the world to Meghan - and Prince Harry - once they find out that Kate's gone out of her way to organise the show."
According to the royal insider, "it'll be a daytime event and guests, including Meghan's pals Jessica Mulroney, Priyanka Chopra, Serena Williams and Amal Clooney, will be treated to an American-style feast."
Kate wants "Meghan and all her friends from across the pond to feel right at home on the big day."