Rep. Joe Kennedy III (D-MA) formally announced his Senate bid on social media Saturday despite Sen. Elizabeth Warren’s (D-MA) endorsement of incumbent Sen. Ed Markey (D-MA).

“Big news: I’m running for US Senate,” Kennedy announced in a social media post. “This isn’t a time for waiting, for sitting on the sidelines, or for playing by rules that don’t work anymore. This is the fight of our lives, the fight of my generation — and I’m all in”:

Big news: I'm running for US Senate. This isn't a time for waiting, for sitting on the sidelines, or for playing by rules that don't work anymore. This is the fight of our lives, the fight of my generation — and I'm all in. I hope you'll join me at https://t.co/7zwvI9aujq pic.twitter.com/WVkNLwCJbg — Joe Kennedy (@joekennedy) September 21, 2019

The Massachusetts congressman told supporters last month that he was seriously considering to launch a senatorial bid against Democrat incumbent Markey, who has been endorsed by his fellow Massachusetts senator, Warren.

“Over the past few weeks I’ve begun to consider a run for the U.S. Senate. This isn’t a decision I’m approaching lightly and — to be completely candid — I wasn’t expecting to share my thoughts so soon,” Kennedy wrote in an August 26 post.

“Family is my first consideration with any big decision like this. Lauren and I have two little kids under the age of four. We’re incredibly lucky to have the support and resources that we do, but like every young family, we struggle daily to balance it all,” he continued.

“I haven’t reached a decision yet — that’s the truth,” he added. “I’m thinking about what I have to offer Massachusetts voters, what is most important in this political moment, and what kind of party Democrats need to be building for the future.”

Some speculated that Kennedy was torn due to Warren’s shining endorsement of Markey:

BREAKING: Ed Markey endorsed by Elizabeth Warren. "We need Ed Markey in the Senate now more than ever." — Ed Markey (@EdMarkey) August 19, 2019

However, Warren has refused to criticize her former law student. When asked about the potentially complicated situation, she said:

I endorsed Sen. Markey back in February. I couldn’t ask for a better partner in the Senate than Ed Markey. He is a good friend. Joe Kennedy is also a good friend. I have worked with him since he was a student of mine. Both he and his wife were my students. I have worked with him as a congressman. I have nothing but the highest respect for him and I have no criticism.

Despite Warren’s endorsement of Markey, Kennedy has signaled strong support for Warren’s presidential bid, telling the Boston Herald that he is “wholeheartedly behind her.”

“If I didn’t think Senator Warren was not only a great senator and would make a good president, I wouldn’t be here. I’m wholeheartedly behind her,” he said.

His formal announcement comes days after freshman Rep. Alexandria Ocasio-Cortez (D-NY) signaled support for Markey, calling the 73-year-old lawmaker the “generational change we’ve been waiting for.”

“Generational change doesn’t mean ‘elect whoever is younger,’” she added, clarifying that generational change is about the “issues.”