No cause of death was given.

Dak had been super close with Jace, the oldest of the Prescott brothers ... and had even just filmed a national Campbell's Chunky Soup commercial with him in 2019.

At the time, Dak said Jace and his other older brother, Tad, meant the world to him ... especially after he tragically lost his mom to cancer in 2013.

"My brothers have always been champions," Dak said. "Them along with my mom ... So now, not having my mom and just having them two, they mean even more."

Dak added, "Family is everything. It's what keeps me grounded when everything else is changing around me I know that's one thing that's always consistent and certain. I'm thankful for them."

Jace was a former football player himself ... he played offensive live for Northwestern State in Louisiana from 2008 to 2010, starting 11 games in his final season.

"The loss of Tad and Dak's brother is devastating," the Cowboys said in a statement during Thursday's NFL draft.

Added team owner Jerry Jones, "We are so saddened that Dak has lost his brother. We want to help him get through this time."

Both Cowboys CEO Stephen Jones and head coach Mike McCarthy also shared their condolences for the QB after the draft.

RIP