Sotheby’s Will Sell Prime Pieces from Sylvester Stallone’s Watch Collection

Besides being an Oscar-winning actor, writer and director, Sylvester Stallone is also one of the most avid and influential celebrity watch collectors in the horology world. But despite his well-known love of wristwatches, one of the rarest models in the Rocky star’s collection—a Patek Philippe Grandmaster Chime—has until now remained a secret.

The sought-after watch, which has never been worn by the actor, is expected to fetch between $2.5 million and $5 million next month when it heads...