Christie’s is having a big Cy Twombly sale this fall—but not, as you might expect, of works by the celebrated artist. Instead, reports the New York Times, the Cy Twombly Foundation is looking to deaccession 11 artworks from the late painter’s personal collection, including important 1960s-era pieces by Andy Warhol, Roy Lichtenstein, Claes Oldenburg, and Bruce Nauman.

These seminal works are all from between 1961 and 1967, and all of the artists were represented by New York’s Leo Castelli Gallery, Twombly’s dealer for more than four decades. Some of the pieces he purchased directly, while Twombly traded his own artwork to acquire others.

“This group represents a long tradition of artists who collected each other’s work,” Laura Paulson, a director of postwar and contemporary art at Christie’s, told the Times. Featuring groundbreaking pop art such as Lichtenstein’s Hot Dog (1964) and Warhol’s Electric Chair (1964), as well as more conceptual work, the collection is expected to fetch around $15 million total.

The two Nauman pieces are expected to be of particular interest, as they are among his earliest works, and were featured in his solo debut at Castelli Gallery. William T. Wiley or Ray Johnson Trap (1967) is one of only three of the artist’s “Light Trap” photos, while Device to Hold a Box at a Slight Angle (1966), a resin sculpture, carries a pre-sale estimate of $900,000–1.5 million.

Christie’s will offer a preview of the sale in London (October 11–16), San Francisco (October 21–25), and New York (November 1–5), before a final viewing at Rockefeller Plaza (November 8–12) immediately preceding the two-day sale on November 12 and 13.