'Meghan conceived just a few weeks after Kate,' a source spills to In Touch, and claims that because Meghan is having multiples, 'they're likely to arrive earlier - which means her due date is around the same time as Kate's.'
'The could give birth on the same day!' a palace insider adds.
According to the publication bombshell report, both duchesses, 36, are preparing to raise the royal cousins as part of 'one big, happy family.'
An insider said, 'Kate and Meghan bonded over the men they married. Now they're bonding over being pregnant together.'
While the pregnancies are the subject of plenty of palace buzz, In Touch reveals the duchesses have only shared the news with close family and friends.
For Meghan, the US publication claims the pregnancy is not just a huge joy but an 'enormous relief.'
'She was a nervous wreck about conceiving,' a palace insider says, not only because of her age but 'because it didn't happen with her first husband,' producer Trevor Engelson, from whom she split in 2013 after two years of marriage and nine years as a couple.
The pressure to give husband, Prince Harry, children 'felt like a huge weight on Meghan's shoulders,' says the source.
'Everyone expected her to get pregnant immediately.'
Meanwhile Prince William, 36, was 'initially shocked when Kate told him he's going to be a dad again', but now he sees it as a 'happy surprise.'
'He and Kate have always wanted four kids,' the source tells.
And this time around, adds the source, Kate gets to share her pregnancy journey with not only her young sister Pippa, 34, who is due with her first child in a few months, but her new sister-in-law, too.
The new duchesses are reportedly loving sharing their journey together.
In Touch reveals Kate 'has penned a pregnancy food list for Meghan that's full of nutritious things to eat and is advising her on how to balance motherhood with life as a royal,' says the source.
Fitness enthusiast Meghan, whose mother Doria Ragland is a yoga instructor, is returning the favour by teaching Kate pregnancy yoga.
The publication adds that the two pregnant women are happily letting their husbands dote on them.
'He brings Kate tea and cookies in bed,' including lavender biscuits which are known to help with nausea.
Kate, adds the source, is 'convinced she's having another girl because she's having the same cravings for sweets that she did when she was pregnant with Charlotte.'
Meghan is hoping for one of each - a boy and a girl - the insider tells In Touch.
'This is a dream come true for both couples.'
The royal family is yet to respond to In Touch's report.
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