Massachusetts Rep. Joseph P. Kennedy III will challenge Sen. Edward J. Markey in a primary, the Boston Globe reported Wednesday evening. Kennedy plans to announce his Senate bid on Saturday, the Globe reported.

Kennedy’s decision comes after weeks of speculation that the grandson of Robert F. Kennedy would challenge fellow Democrat Markey, who is serving his the first term. Kennedy had filed a statement of candidacy with the Federal Election Commission in late August.

“I’ve been running on the issues of climate change and income inequality, a woman’s right to choose, and gun safety. The response I’ve been receiving is absolutely fantastic across the whole state,” Markey told CQ Roll Call when asked to respond to Kennedy’s challenge as he walked off the Senate floor Wednesday night. “I’ve been crisscrossing the state, the response has been tremendous and I’m going to be out there campaigning on these issues for the next year.”

Markey declined to confirm that Kennedy informed him personally about the primary challenge, directing additional questions to his staff.

Kennedy’s office has not yet responded to requests for comment.

Markey has sought to head off a primary challenge by touting his progressive credentials. He has recently been endorsed by New York Democratic Rep. Alexandria Ocasio-Cortez and Massachusetts Sen. Elizabeth Warren.

Ocasio-Cortez and Markey have co-authored the Green New Deal, a sweeping series of programs aimed at combating climate change. Kennedy has also been an ardent supporter of Warren, his former professor at Harvard Law School, who holds the Senate seat formerly held by two of his great-uncles, Edward M. Kennedy and John F. Kennedy.

The race could be generational clash between Markey, 73, and Kennedy, 38, whose ties to the Kennedy political dynasty will likely boost his name recognition. He is the grandson of Robert F. Kennedy.

Kennedy has made headlines for his ambitions for higher office before. His calls last year for the Democratic party to adopt a bold new economic agenda he termed “moral capitalism” spurred speculation that he would run for president.

Kennedy, who was once a staunch opponent to legalizing marijuana, changed course in 2018, endorsing nationwide legalization in a Boston Globe editorial.

A primary challenge, even an unsuccessful one, could raise Kennedy’s profile and make him a stronger candidate for the Senate should Warren resign for the presidency.

Other Democrats in the race include Shannon Liss-Riordan, a labor-rights lawyer.