Arnold Schwarzenegger's Secret Son -- Walking (Very) Tall Before Dad's Book Release

With Arnold Schwarzenegger's tell-all autobiography about to come out, it seems only fitting that his all growed-up love child Joseph Baena and his baby mama/former maid Mildred Baena would be spotted out in Bakersfield, CA on Thursday.

As we reported earlier, Arnold says his affair with Mildred was the "stupidest thing" he did during his marriage to Maria Shriver and revealed he has not shown her the book yet either.

Fun fact: Schwarzenegger's book comes out on Monday ... the day before Joseph's 15th birthday.