The out-of-wedlock granddaughter of a late British art collector is poised to claim half-ownership of a $1 billion collection of paintings, sculptures, tapestries and other objects that were left to New York University in 1994, Page Six has learned. The school has called the treasure trove — amassed by Sir Arthur Acton and bequeathed to NYU by his son, Sir Harold Acton — part of the “most magnificent gift” ever to an American university.

But a July 17 ruling in a decades-long court battle in Italy said that DNA proved Acton also left another heir — the late Liana Beacci, daughter of Arthur’s mistress, Ersilia Beacci. And Liana’s daughter told Page Six she’s “100 percent certain” the court will also posthumously award her mom an equal share of the more than 6,000 artworks, French dresses and Baroque furniture.