Arnold Schwarzenegger hits the gym with Joseph Baena: See his buff 20-year-old son

Jennifer Kline, AOL.com

The Schwarzeneggers take "like father, like son" to a new level!

Arnold Schwarzenegger offered birthday wishes to his 20-year-old son, Joseph Baena, with an Instagram photo of the two at the gym -- and just like his dad, Joseph definitely isn't slacking.

"You're a fantastic son and a great training partner," Arnold captioned the pic. "You get stronger and smarter every year and I'm so proud of you. I love you."


Joseph is the "love child" of Arnold and his former family housekeeper, Mildred Patricia Baena. He was only 13 when Arnold's then-wife of 25 years, Maria Shriver, discovered the torrid secret.

Days before celebrating Joseph's birthday, Arnold also heaped praise on his son Christopher, who also just turned 20.

"You're a wonderful student, a hilarious and kind soul, and a fantastic son," Arnold wrote alongside a throwback photo of the two sharing a father-son smooch. "I'm so proud of you, I love you, and I can't wait to see what's next."

Christopher was born on September 27, 1997, and Joseph was born days later, on October 2 of the same year.