"You are my favorite person and have taught me everything I know about love," Selma Blair wrote in the sweet tribute to her only child, son Arthur

By Jen Juneau
June 07, 2019 09:38 AM

Selma Blair‘s little boy is moving on to second grade — and she couldn’t be prouder.

The actress, 46, shared a quartet of mother-son photos to Instagram late Thursday evening, showing the pair walking and posing together over the years from the time 7½-year-old Arthur Saint was a baby.

“To my son on his last day of first grade. I will hold your hand, I will help hold the light for you. I will lift you up if ever you need me,” she began the touching social-media tribute to Arthur, her only child. “You are my favorite person and have taught me everything I know about love.”

“I am so proud of who you are. I can’t wait to reach for your hand,” Blair continued. “And you will be right here. Soon. Soon. Always, your mom. You are a wonderful person.”

She ended the post with heart emojis and a series of hashtags: “#arthursaintbleick,” “#Fbf,” “#givemeyourhand,” “#childrengetolderandimgettingoldertoo” and “#sotakethislove.”

Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Parents newsletter.

Blair revealed in October that she had been diagnosed with multiple sclerosis, and has since been open about how the condition has affected her day-to-day life, including her dynamic with her son.

Selma Blair and Arthur Saint
Credit: Michael Buckner/Variety/REX/Shutterstock

“After the MRI, I said, ‘I have something called multiple sclerosis,’ and he almost cried and said, ‘Will it kill you?’ ” the American Crime Story actress told Robin Roberts in a February sit-down for Good Morning America — her first television interview since revealing her diagnosis.

“And I said, ‘No. I mean, we never know what kills us, Arthur. But this is not the doctor telling me I’m dying,’ ” recalled Blair. “And he was like, ‘Oh. Okay!’ ”

Selma Blair and son Arthur
| Credit: Alberto E. Rodriguez/WireImage

RELATED VIDEO: Jaime King Says Best Friend Selma Blair Is “So Brave and So Strong” for Talking About Her MS Journey

Blair shared with Roberts that she didn’t have a problem “at all” being honest with her only child about her condition, especially considering he sensed on his own that things had changed.

“I always want him to feel safe, never responsible for me, but he had already seen that I was falling and doing [different] things, and I was always laughing,” she said.

“And he’d imitate me,” added the Cruel Intentions actress. “I’d be like, ‘That’s fine, but don’t do that [outside] of the house. People will think you’re a jerk.’ ”

Selma Blair and son Arthur
| Credit: Selma Blair Instagram

Blair brought Arthur along as her date to the 26th annual Race to Erase MS gala last month, where she was being honored. While on the red carpet, the pair held hands as they posed for some adorable mother-son photos, with Blair rocking a custom Christian Siriano tuxedo with a black cane.

As she took to the stage inside the event, the proud mother shared that her son “is the reason for everything.”

“I have to say that I am afraid that I will fall, and I have the best ‘fall-bearers’ in the world,” she continued, praising her son as well as her longtime pal Sarah Michelle Gellar.

“My dream is that I get to be a useful mom, as long as this kid wants me,” she shared at the conclusion of her remarks after leaning down to pick up her son, before joking, “which is about one more year.”