New bosses generally bring in their own people. Nevertheless, the art world was surprised to learn on Monday that the new owner of Sotheby’s, Patrick Drahi, had named Charles F. Stewart as his new chief executive officer, replacing Tad Smith just two weeks before the start of the fall auction season.

“It is clear with this news that Drahi’s vision is to take Sotheby’s in a new direction,” said Abigail Asher, a longtime art adviser. “It will be interesting to see what these changes bring.”

In a news release, Sotheby’s said the appointment was “effective immediately,” though it suggested that Mr. Smith — who has served as C.E.O. since 2015 and declined through a spokeswoman to be interviewed — had no hard feelings. “Underscoring his confidence in Sotheby’s long-term success,” the release said, “Mr. Smith will become a shareholder of the company and act as a senior adviser to Mr. Stewart.”

The choice of Mr. Stewart, 49, is not entirely surprising. He comes to Sotheby’s from Altice USA, a communications and media company that is also owned by Mr. Drahi, and the two are said to be comfortable with one another. Mr. Stewart has spent the last three years as co-president and chief financial officer of Altice USA. He previously served as chief executive of Itau BBA International plc., the European platform of the Latin American corporate investment bank, and previously spent 19 years as an investment banker at Morgan Stanley.