Arnold Schwarzenegger has paid tribute to his lovechild Joseph Baena on his 19th birthday.

Arnold Schwarzenegger and Joseph Baena

Arnold Schwarzenegger and Joseph Baena

While the 69-year-old action star rarely talks publicly about Joseph - who he fathered with his housekeeper Mildred Baena while still married to Maria Shriver - he took to Instagram on Sunday (02.10.16) to share a heartfelt message.

Posting a picture of him and Joseph together, he wrote: "Happy birthday, Joseph. Great student, great athlete. I'm proud of you and I love you!"

In the image, the pair are enjoying beers at Oktoberfest in Munich, Germany.

Arnold separated from Maria in 2011 after he confessed that Joseph was his son and though he regrets the end of his marriage, the star previously insisted he has no desire to alter his "mistakes and failures".

Asked if he'd do anything differently if he could go back in time, he said: "I don't know if I would change anything. I'd leave it alone, even with the mistakes I made.

"Overall - even with the failures - my life has been blessed and I am a happy person and I wouldn't change my life with anyone else's."

Instead, Arnold - who is now dating Heather Milligan, 41 - tries to learn from his mistakes.

He added: "I've learned to be positive; and to get up and make sure that you undo as much of the damage that you can and that you think twice before you make mistakes. And think about what effect they have on other people.

"Everyone has their setbacks and everyone had times when they fell.

"What I did all the time is just get up and not whine about it."

And the 'Expendables 3' actor is thankful he now has a "wonderful" relationship with his ex-wife, with whom he has four children.

He said: "We both behaved like grown-ups and said maybe we have disagreed on some things and I screwed up on some things, but let's raise the kids together and show harmony so I can go to her house and we celebrate and she can come over to my house and celebrate if it's Mother's Day or birthdays or Christmas or whatever.

"Now I have a wonderful relationship with Maria. There are no fights. We talk all the time on the phone.

"We are responsible parents and we know the only way it works is if we work together and that is going really well."