Kim Kardashian has sent Britain's Duchess Catherine a maternity gift along with a letter, but she is said to be disappointed not to have received an immediate response from the brunette royal.The pregnant reality star was "really excited" to find out the British royal - who was known as Kate Middleton prior to her nuptials with Prince William - is due in July, the same month as the 'Keeping Up with the Kardashians' star, so she sent the duchess a letter and mystery present.A source said: "When Kim found out the pair had similar due dates, she got incredibly excited."She had her PA write a kind, warm note to Kate, enclosing a gift for the future heir to the throne and explaining they were both due in July."While Kim is reportedly disappointed she hasn't received an immediate reply from the duchess, she was keen to let her know she will be decorating her little one's bedroom with rubies and moonstones, as they are associated with the Cancer star sign, which both babies will be if they are born between June 21 and July 22.The insider added to the Daily Mirror newspaper: "Kim has now employed a top astrologer in Paris to draw up all the qualities of a 2013 Cancerian baby and is busy sourcing all the icons associated with Cancer the crab for the baby's room."It will also be decorated, with rubies and moonstones - Cancerian gems."This was a piece of advice she was particularly keen to relay to the Duchess of Cambridge and was a little saddened not to have received an immediate response."A Buckingham Palace spokesman has declined to comment on the news.