Selma Blair's Son Arthur Looks All Grown Up as She Shares Rare Photo of Him on Mother's Day: 'Proudest Mom'

Selma Blair is celebrating Mother's Day with a rare look into her and her son's life.

On Sunday, May 12, the Legally Blonde actress, 51, shared a post to Instagram as she reflected on her relationship with her son, 12-year-old Arthur Saint.

In the photo, Blair and Arthur can be seen posing on an outdoor patio, as the pre-teen — looking all-grown-up — sits in an armchair and Blair crouches down beside him, as her service dog Scout sits on the ground in front of them.

"This is the first Mother’s Day in ages, where my son lets me capture him for a photo. And my love is boundless," Blair wrote in the caption. "Thank you Arthur. I’m the proudest mom. Happy Mother’s Day mamas ♥️."

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

Although Arthur — who Blair shares with her ex, fashion designer Jason Bleick, whom she dated from 2010 to 2012 — seemingly doesn't like to be photographed by his mom too often, Blair has been candid about her parenting journey, as well as her love for her son.

Speaking exclusively with PEOPLE back in November 2023 at Glamour's Women of the Year Awards the actress joked about what exactly Arthur thought of her being honored at the ceremony.

"I can't remember. My son probably said, 'Are you getting paid? Can I have money?' " she laughed. "I imagine that's like what he always says."

"Oh, typical boy. Yeah, that's why we celebrate females," she joked at the time. "No, my son is perfectly 12. I'm sure he is proud."

She also took time to celebrate his 12th birthday back in July, sharing a collection of photos of Arthur. Alongside the post, she wrote, "My Saint, Arthur, happy birthday 🎂."

"This has been the most incredible life with you. Forever my favorite, I know you are going to have the best year yet," she continued. "I am so proud of who you are and have become. Usually 🦁. The most adorable little kid has grown into a 12 year old!!!! 🐣🦅. I love you and I like you. Massively. 💛 mom."

Back in October 2021, Blair opened up about her son's involvement in her health since her multiple sclerosis diagnosis in her documentary Introducing, Selma Blair. One scene from the film showed Arthur shaving Blair's head prior to her stem cell transplant procedure in 2019.

"It was to have him be a part of it, help him be in control of maybe like a first image of Mom looking different," Blair told Entertainment Tonight at the time, speaking about the moment from her documentary. "That was pretty easy and a nice moment, and it makes me feel better knowing Arthur has a say — not a say, really, but is included."

In 2022, Blair also made an appearance on Dancing with the Stars — and Arthur showered his mom with compliments at the time.

"I'm really proud of her," he told Access Hollywood following her stint on the show. "It's just wonderful that she does this stuff and moves around."

"It was amazing," he added. "Even the judges were moved by it."