Kate Middleton has been at home with mother Carole Middleton, 57, over Christmas - and the pair are in constant touch.
But when Carole can't be by her pregnant daughter's side, she knows Kate has Camilla, Duchess of Cornwall for support.
'Kate spends hours each week calling her mum,' says our source. 'She gets lonely without her, so it's nice for Carole to know Kate's got Camilla.'
In fact, we can reveal the two are so close, Camilla, 65, knew about Kate's pregnancy before the Queen.
Prince William, 30, told his gran when Kate, 30, was rushed to hospital suffering extreme morning sickness on 4 December.
But our source says: 'Camilla was the first outside of Kate's immediate family to know.'
Camilla's help will be all the more important as Wills is expected to return to work as an RAF Search and Rescue pilot in Anglesey soon.