Niarchos has made plenty of additions to his father's legacy. He was suspected as being the anonymous buyer of Vincent van Gogh's "Self-Portrait", at a November 1998 Christie's auction; it sold for $71.5 million. He was certainly at the auction and was revealed as the anonymous buyer of Jean-Michel Basquiat's 1982 Self-Portrait, which closed at $3.3 million. In 1994, he bought Andy Warhol's Red Marilyn, at Christie's for $3.63 million. Andy Warhol's skull portraits are from Niarchos' CAT scan. Warhol completed these works in 1985, using silkscreens made from CAT-scan films of the skull of Philip Niarchos, who commissioned the Artist to paint his portrait. Niarchos is mentioned throughout The Andy Warhol Diaries. Warhol shares details of the dysfunctional relationship Niarchos had with the divorced and widowed socialite Barbara (née Tanner) de Kwiatkowski. Her married name was Barbara Allen at the time of her relationship with Niarchos; now she is the widow of Henryk de Kwiatkowski.