Arnold Schwarzenegger's family is celebrating a big milestone.

The "Terminator" star turned 74 on Friday and several of his children took to Instagram to wish him a special day.

"HAPPY BIRTHDAY DADDY! I love you so much and can’t wait to celebrate you!" wrote his daughter Katherine alongside several sweet throwback pics. "Have the best day ever!!"

Included in her post was a pic of a young Katherine riding horses with her father, another of the two embracing one another, a snapshot from a day in the pool, another lounging on a hammock, another of baby Katherine looking at a birthday cake and finally a photo of the young girl cuddling her father.

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Arnold Schwarzenegger turned 74 on Friday and his children celebrated him on social media.  (Getty Images)

The actor's son Joseph Baena also shared a photo of himself and his famous father holding up their drinks at a restaurant.

"Happy Birthday Dad!" he captioned the loving post. "I hope your pump was juicy and may your day be filled with lots of schnitzel, schnapps and stogies!!!"

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Patrick Schwarzenegger, also an actor, shared a video of his old man lifting weights.

"Happy Birthday pops! Can’t believe you became a grandpa this past year," he said in the caption, referring to Katherine's daughter Lyla with Chris Pratt. "Can’t wait to see what happens this year!"

Arnold Schwarzenegger's famous children Katherine and Patrick shared sweet birthday messages online. (Getty Images)

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He added: "Also… i have no idea how your 74 today & still pullin this weight. I truly hope I’m half as strong physically & mentally when I’m your age."

While the star's children are obviously fond of their father, it seems they weren't very big fans of his previous job as a Republican governor of California.

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"First of all, I think it is very important to let everyone know how much you kids hated my job," he said during an interview on Katherine's Instagram show "Before, During and After Baby" in June. "It was one of those kind of odd things where I just thought that: ‘Oh, my kids will be so proud of me being governor now, and all this stuff, but I don’t think that you guys really kind of connected with that," Arnold said. "I think you were so used to what we were doing when I was on a movie set."