The Pepperdine graduate, whom Schwarzenegger shares with his former housekeeper Mildred Baena, took to social media to wish his father a happy 72nd birthday on Tuesday.
"BIG happy birthday to the best training partner in the world!" Joseph Baena wrote."Love you dad."
The photo shows the father-son duo, both in outstanding shape, working out together at Gold's Gym. Schwarzenegger points to his son with pride as he gets in an arm workout.
Schwarzenegger's other children also used social media to honor their father on his special day.
Patrick Schwarzenegger, whose mom is Maria Shriver, posted a photo of his famous dad celebrating along with Patrick's siblings Christina, Christopher and Katherine (who is married to Chris Pratt).
In the photo, the actor poses with a cake that shows him smoking a cigar in a hot tub.
"The cake," Patrick wrote with laugh-crying emojis. "Happy birthday big guy."
Recently the actor made an appearance at Comic-Con with Linda Hamilton and the stars of the original 1984 "Terminator," to debut new footage for "Terminator: Dark Fate" (in theaters Nov. 1).
"Of course, I needed to come back. I'm addicted to 'Terminator,'" Schwarzenegger said, adding that James Cameron's first film "launched my action-movie career. From that moment on, everything changed."
Contributing: Brian Truitt
This article originally appeared on USA TODAY: Arnold Schwarzenegger's son Joseph Baena posts sweet birthday tribute