Padres CEO Erik Greupner shared the heartbreaking news on social media .... saying in a statement Seidler was "beloved" in the org.

A cause of death was not revealed ... however, Seidler -- a two-time cancer survivor -- had undergone health issues recently, revealing in mid-September he had needed a medical procedure in August that would force him to miss the rest of his team's 2023 games.

"Today, our love and prayers encircle Peter's family as they grieve the loss of an extraordinary husband, father, son, brother, uncle, and friend," Greupner said.

"Peter was a kind and generous man who was devoted to his wife, children, and extended family."

Seidler bought the Padres back in 2012 with his uncle, Peter, and Ron Fowler after they created the O'Malley Group.

Fowler was named the ownership group's executive chairman ... but in 2020, he transferred his role to Seidler. Fowler still remains as Padres vice chairman.

Outside of baseball business, Seidler was big on helping the homeless in San Diego ... joining the Lucky Duck Foundation as one of the board of directors.

"His impact on the city of San Diego and the baseball world will be felt for generations," Greupner said. "His generous spirit is now firmly embedded in the fabric of the Padres."

"Although he was our Chairman and owner, Peter was at his core a Padres fan. He will be dearly missed."

The Padres will allow fans to pay respect to Seidler at Petco Park's Home Plate Gate on Tuesday afternoon.