The British designer created a gown for Pippa to wear to the evening reception of her sister Duchess Catherine's wedding in April and the 28-year-old party planner was such a dream to work with that Alice would love to create a dress for her if Pippa's boyfriend Alex Loudan ever pops the question.
She told Britain's Daily Telegraph: "I'd love to dress Pippa for her wedding when it happens.
"She's so beautiful - she's perfect and her bum is perfect - it would be wonderful. Both the girls are impeccably mannered."
Pippa has been dating former cricketer Alex, 30, for more than a year and friends recently revealed he is such a hit with her family that parents Carole and Michael, brother James, sister Catherine and her husband Prince William hope the couple will marry.
A source said: "William, Catherine and Pippa's parents adore Alex. They trust him and see him as one of the family. They'd be very happy if he slipped a ring on Pippa's finger."