WEST PALM BEACH, Fla. — Tom Seaver, the Hall of Fame pitcher and greatest Met of all time, has been diagnosed with dementia and retired from public life, his family announced Thursday.

The news comes as the Mets approach the 50th anniversary of the 1969 championship team that Seaver, nicknamed “Tom Terrific,” pitched to a World Series win.

Seaver’s family said in a statement released by the Hall of Fame that the 74-year-old will continue to work in his beloved vineyard in California, but will no longer make public appearances.

Seaver has been dealing with cognitive issues for years, but attributed them to Lyme Disease. Former teammate Art Shamsky called Thursday’s news “just another kick in the gut.’’

Seaver’s family asked for privacy for Seaver, who won three Cy Young Awards and 311 games during his career. The right-hander out of Fresno, Calif. and USC struck out 3,640 batters and had a lifetime ERA of 2.86 while being selected to 12 All-Star Games.

“We’ve been in contact with the Seaver family and are aware of his health situation,” Mets COO Jeff Wilpon said in a statement. “Although he’s unable to attend the ’69 Anniversary, we are planning to honor him in special ways and have included his family in our plans. Our thoughts are with Tom, Nancy and the entire Seaver family.”

Seaver won NL Rookie of the Year honors with the last-place Mets in 1967 and was an integral part of the franchise’s first championship season in 1969, leading the league with 25 wins and finishing MVP runner-up.

Despite his star power, tensions between Seaver and the team rose over a contract dispute, leading to a June 15, 1977, trade dubbed the Midnight Massacre that sent him to the Reds as part of a five-player deal, though he was traded back to Queens in 1982.

Seaver also pitched for the White Sox and finished his 20-year career with Boston in 1986. He was a first-ballot Hall of Famer in 1992, receiving 98.8 percent of the vote. It was the highest percentage of votes until Ken Griffey Jr. broke it in 2016 with 99.3.

Former teammates remembered Seaver on Thursday, with Ed Kranepool calling him “a man’s man.”

“He did everything with class and dignity,’’ Kranepool said. “Everything he did on the field was 100 percent. He was one of a kind.”

“My wife Angela and I said our prayers to Nancy and Tom,’’ Cleon Jones said in a statement. “I was proud to be his teammate. No one competed like Tom Seaver.’’

Shamsky also praised Seaver’s competitiveness.

“It wasn’t just that he was a great pitcher, but he was smart and he wanted nothing more than to beat you, even if he didn’t have his ‘A’ game with him,’’ Shamsky said. “I played with him and against him and I never saw a guy quite like that.”

Seaver’s diagnosis comes 13 months after fellow 1969 Met Buddy Harrelson revealed to The Post that he’s dealing with Alzheimer’s. Kranepool, meanwhile, continues to search for a kidney donor.

Manager Mickey Callaway, after the Mets lost to the Nationals, 6-4, at Ballpark of the Palm Beaches, said he never got to meet Seaver, but “heard many, many stories and just the legacy that is around the Mets clubhouse, around the Mets organization is unbelievable.”

— Additional reporting by Kevin Kernan and Mike Vaccaro