"Happy Birthday to my lovely daughter! 28 years old and everything we've ever hoped for in a child," the Whose Line Is It Anyway? star wrote alongside a photo of his only child along with his wife, Debra McGrath.
However, what started out as a beautiful message of love and support turned hostile thanks to a few hateful people on the social media platform.
Luckily, Colin had the support of his fans — who applauded the improv actor for showing his trans daughter and the LGBTQ community love. "Thank you for supporting your lovely daughter and the trans community. I work with homeless trans youth and the main reason they are homeless is related to family rejection. We need more parents who understand and love their children without condition. Thank you for being that kind of parent," one follower wrote.
Another added, "I’m a trans woman, and today is the first day my mom called me her daughter. Thank you for being supportive of your daughter! Supportive parents make all of the difference."
Colin also called out the haters, writing, "Thanks to the fans of this page for being supportive and human. To the trolls, my thoughts and prayers to your body for losing it's mind and soul so tragically."
This is not the first time Colin, 60, has defended his daughter in public. Last year, he opened up about how improv — and the "yes, and..." rule — helped him accept his daughter after she came out as trans.
"We've started saying yes — within limits — and it's taken us to these amazing places and amazing people," he explained on The National. "So I do think improv actually did help with this."
He continued, "You accept what someone has given you and you build on that."
He also uses his signature sense of humor to spread awareness about the trans community. "My 90-yr-old mother-in-law and 87-yr-old mother love and acceptance of our trans daughter warms me. Wonder why some who are younger can't," he tweeted at the time. "The negative is that my mom refers to the community as BLT. It's a learning curve."
So, who is Kinley Mochrie?
Kin, as her family and friends call her, opened up about the struggles of coming out to her parents in 2016, but revealed she was never worried about losing their support.
"It was fairly straight forward," she said on ET Canada. "There were challenges that came with it... I know there was some difficulties around getting used to the name change."
Born Luke Mochrie, Kinley actually asked her parents for help when it came time to pick out her new moniker.
"I said to my parents, 'I would like to know what names you like and what names you would give me now,' and they came back to me the next day with a list of 20 names," she added. "Slowly, we whittled it down to about five and then slowly got to... I don't know, there was just something about Kinley."
As always, Colin has been his daughter's biggest cheerleader. "This is my child, this is the exact same person, with a new coat," he said before jokingly adding, "All you want when you have a child is for them to be safe, to be happy, and to be better than you."
And she is doing just that. Kinley identifies as a bisexual non-binary trans woman and has been open about her gender dysphoria on Instagram. "Dysphoria may be strong today, but it won’t prevent me from uploading this adorable shot of me and this sweet boy," she captioned a selfie with her pup. "We’re a cute pair!"
Plus, it looks like Kinley, who studied screenwriting at the New York Film Academy, is following in her funny father's footsteps and is currently working at famed sketch comedy theater Second City in Toronto.