Kaitlin Olson, the star of “High Potential,” announced the death of her father Don Olson on social media Monday.

Calling him “my first love, my first protector and my forever favorite person,” the actress, 50, posted the news on Instagram.

“Honestly it feels a little gross to bring this to social media. It’s too fragile and too private. But nothing feels more wrong than to just move on with life as if the worst thing in the world didn’t happen,” she posted. “As if everything that matters didn’t just suddenly end.”

She added that her father “fought so hard and so long to stay with us.”

“I hate words right now. None are good enough to describe who he was,” she posted. “The luckiest thing to happen to me in this lifetime was getting him as my dad. Maybe the second was the gift of holding him on his way out. I love you, daddy. I will keep all my promises. Just like you.”

Olson’s costars Mary Elizabeth Ellis, Jimmi Simpson, and Steve Howey were among those to show their support on the emotional post.

Olson shares two teenage sons with Rob Mac, her longtime husband and “Always Sunny” costar, and he also reacted to the loss of his father-in-law.

“Words are impossible,” he wrote on Olson’s tribute. “There is no one like him. My whole goal in life is to be half the man he was. I’ve never seen a person love someone the way he loved you. I am so grateful that he lived and so proud that I got to be his son for the past 17 years.”