It is thought Harry's girl will not be joining the royal threesome, and will stay behind in the UK, according to enstarz.com.
If the reports are true, it will be the second wedding in just weeks that Prince Hazza has attended sans his girlfriend.
But, according to enstarz.com, the move is likely to have been decided on together, with the pair wanting to enjoy their privacy for as long as possible.
A source recently said: "Harry and Cressida have made a point of talking about marriage and what changes they're going to have to make to their life of late. According to friends of Cressida's, the couple have decided to try and keep their semi-normal lifestyle as long as physically possible."
The prince recently joined the Duke and Duchess of Cambridge at the wedding of Lucy Meade and Charlie Budgett at St Mary the Virgin church in Marshfield, Gloucestershire at the end of March (pictured above).
Lucy is the sister of James Meade, one of William's oldest friends from Eton. James was also William's best man and gave a speech at the Royal wedding.
The upcoming wedding in the US will see Memphis-born Elizabeth Wilson marry Guy Pelly, who is a good friend of Prince William and Prince Harry, and who owns a nightclub in London.
It is thought the brothers will be ushers at the ceremony, to be held on 3 May.
Prince William and Duchess Kate will no doubt still be tired from their three-week tour of New Zealand and Australia.
LOVE HAZZA? See why we're all head over heels for Prince Harry in our gallery below:
MORE CRESSIDA! See exactly why Ms Bonas has stolen the prince's heart in our style file gallery below: