"I could say that I am so proud of the person you are becoming...but the truth is I have always been proud of you," the actor said on Tuesday next to a photo of Meadow Walker and Diesel's 4-year-old-daughter Pauline Sinclair.
"Happy Birthday Meadow! I know it's your 21st and you wanted to go big in Japan, but the family has a cake waiting for you when you get home, so hurry. Love you kid. Uncle Vin," Diesel continued.
Meadow Walker responded to Diesel's post with a comment. "Thank you so much. I can't wait to see you soon. And my little angels. Love you," she wrote.
Diesel and Paul Walker were friends and co-starred together in the Fast & Furious film series before the Hollywood star died in a car crash in November 2013 at the age of 40.
Meadow Walker reached a wrongful death settlement with Porsche in October 2017, the maker of the vehicle Paul Walker was in that also killed his friend, Roger Bodas.