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Pippa Middleton might get a royal title of her own!

British tabloid The Sun claims that Duchess Kate's sexy sister is in a serious relationship with her longtime pal George Percy -- an Earl worth $400 million who will one day be the Duke of Northumberland.

Middleton, 28, and Percy, 27, have been friends since their college days at Edinburgh University. Pippa and George have been photographed together numerous times -- including a summer 2011 weekend trip with pals in Spain -- but the Sun reports that things became romantic during a New Year's Eve bash thrown by the Middleton family.

Middleton and beau of two years, banker Alex Loudon, called it quits for good last fall.

As the future duke, Percy (who was a royal page to Kate's grandmother-in-law Queen Elizabeth) will be entitled to 100,000 acres, 100 tenanted farms, a country estate in Surrey and a mansion in London, the Sun reports. Perhaps the most stunning property in the family is Alnwick Castle, which was used in the Harry Potter films as Hogwarts School.

If Middleton were to marry Percy, she would one day enjoy the title of Duchess.

Percy is "completely in love with her," a source is quoted in the Sun as saying.