Smith joked about his son's love of superheroes, sharing a photo of him wearing a Spider-Man costume.
"Happy Bday, Jaden. 20 Years Old ~ WHOA," the Men in Black star wrote. "And Wait... I don't know what the big deal was when you wore a White Batman Suit to Prom? You have ALWAYS worn superhero suits on your dates!"
Coincidentally, Jaden's co-star in the photo is Jordyn Woods, best known today as Kylie Jenner's best friend.
Smith's comment also referenced the infamous white Batman suit Jaden wore to Kim Kardashian and Kanye West's wedding in 2014, when he was 16. Jaden recycled the suit a year later when he went to his high school prom with friend Mecca Kalani.
In an interview with GQ in 2015, Jaden admitted he would wear a Batman suit or Spider-Man suit with duck boots as a kid and "never take them off." As for his unique Batman formal wear, he said he wanted to protect everyone at the wedding.
"I wore the Batman suit to heighten my experience at the wedding and prom which was fun, but also at the wedding I felt as though I needed to protect everyone there and needed to have the proper gear to do so," Jaden explained.
He also said his style icons are Batman, Robin, Nightwing, Superman and West.
Jaden's mom, Pinkett-Smith, also celebrated her son's birthday by sharing a photo of him while he was still in diapers.
"Jaden is 20 today and I'm ALL in my feelings about it. I've enjoyed watching him get older until the teen dropped off the number lol. You're still my baby Jaden ... I really don't think that will ever change:) Happy Birthday my love. Thank you for always making my heart smile," Pinkett Smith wrote.
Pinkett Smith and Smith are also parents to Willow, 17. Smith also has a son from his first marriage to Sheree Zampino, 25-year-old Trey.
When Willow's birthday comes up in October, the family will be sure to celebrate in a different way. Pinkett Smith said on her Facebook Watch show Red Table Talk that the siblings could not be more different.
"Jaden and Willow have always been different. They were born that way," Pinkett Smith said. "A lot of people think that it came from my rearing, but no, it just so happened that that's how they came into the world and I had to get in order. I had to be open enough to receive it."
Jaden starred alongside his father in After Earth (2013) and The Pursuit of Happyness (2006). He also released his new album, SYRELand, this weekend.
Photo credit: Michael Kovac/Getty Images for Netflix