"That's my dad!": Gus Walz tearfully cheers on his father as he accepts Democratic VP nomination

CHICAGO -- Gus Walz sat in the front row for the biggest moment of his father's life, and his pride exploded out of him.

"That's my dad!" the 17-year-old yelled. He stood, tears streaming down his face, and pointed to his father, Tim Walz, the governor of Minnesota, who was accepting the Democratic nomination for vice president in a speech to thousands of people in a packed arena and millions more watching at home.

The teen's exuberance captured hearts and went viral, becoming perhaps the defining image of his father's address and further humanizing a running mate picked by Vice President Kamala Harris in no small part for his everyman appeal.

RELATED | All about Tim Walz's wife Gwen Walz and 2 kids: Meet the VP pick's family

Gus wept through much of his father's speech, and when it was over, climbed on stage with his family and wrapped his dad in a tight bear hug, burying his face in his shoulder.

Gus is a high school senior. His parents recently disclosed to People magazine he has a non-verbal learning disorder, ADHD and an anxiety disorder. But they called his condition "his secret power" and said he's "brilliant" and poised for success. He got his driver's license last fall.

When Tim Walz was elected governor, Gus cheered because it meant he could get a dog. They adopted a black lab named Scout a few months later.

RELATED | Tim Walz DNC speech: Read the full text of the vice presidential nominee's address

Gus Walz is getting his own turn in the spotlight after his older sister, 23-year-old Hope Walz, delighted Americans with the playful social media videos she filmed with their dad.

Tim Walz talks often about the fertility treatments his wife, Gwen, underwent to get pregnant with Hope, a journey he says inspired her name. As he told the story Wednesday, Hope made a heart with her hands and held it over her chest.

"Hope, Gus and Gwen," Walz said to his family, "you are my entire world, and I love you."