Patrick Schwarzenegger and his half-brother, Joseph Baena, were seen working out together.
Patrick, 27, and Joseph, 23, were spotted working out together on the Santa Monica stairs with Joseph's girlfriend, Nicky Dodaj.
Patrick wore a backwards baseball cap and shades with a long sleeve shirt and shorts. Joseph also went casual in a gray T-shirt and shorts.
The half-siblings have not been spotted out publicly before, though Arnold has publicly supported Joseph many times after it was revealed in 2011 that he was his son.
Patrick is one of four children Arnold shares with his ex-wife, Maria Shriver. Joseph is the child of Arnold and his former housekeeper, Mildred Baena.
Joseph has followed in his famous dad's footsteps to become a body builder. He also regularly praises the actor on social media.
"Wishing the Happiest Birthday to my Dad! You are and will always be 'Número Uno,'” Joseph captioned a sweet childhood throwback with the actor last July.