Middleton, 28, the younger sister to the Queen's granddaughter-in-law, Kate Middleton, is back in a serious romance with her old flame, George Percy, reports Duncan Larcombe, royal editor for UK's The Sun and an ABC News contributor.
The rekindled romance, the two met at Edinburgh University and had a fling during their senior year in 2008, could see Middleton following in her sister's footsteps and becoming a royal too.
Percy, 27, is heir to the Duke of Northumberland, one of Britain's grandest and richest titles. As a boy, he served as a page to the queen, according to Larcombe.
His family's estate is valued at more than $500 million and includes ownership of Alnwick Castle, familiar to Americans as the setting for Hogwarts School in the Harry Potter movies.
A source close to the pair told Larcombe, "George is very smitten and completely in love with her."
Said to be factors in the split were Middleton's growing fame - she was dubbed "Her Royal Hotness" and became a target of paparazzi after she wowed onlookers as a bridesmaid at her sister's wedding in April - and her relationship with Percy.
"Pippa has always been close to him," the friend of Percy and Middleton told the Sun. "There is no doubt this was a huge issue for her ex-boyfriend Alex."
Percy was seen helping Middleton get over her split with Louden, but the two insisted they were "just friends" at the time, according to the Sun.
The now-couple reportedly made it official after pairing up at the extravagant New Year's Eve party Middleton threw at the her family's Berkshire home attended by Prince William and Kate.
"Pippa sat herself next to George at supper and made sure she was hanging off his arm all night," according to the Sun. "And then she made her move."
Middleton, who lives in London and works for her family's party planning business, will bring her expertise to print in a new book in 2012.
Percy runs a renewable energy business and is also the beneficiary of a trust fund that will guarantee him an income of nearly $400,000 each year, thanks to his royal pedigree, according to the Daily Mail.
ABC News' Nick Watt and Carolyn Durand contributed reporting.