Meadow Walker, 21, recently posted a selfie with Diesel's three children, Hania, 12, Vincent 10 and Pauline, 5.
The three young men are seen smiling behind Walker, who appears to have taken the photo, which he shared on his verified Instagram account.
"Family, forever," says the caption.
Diesel is tagged in the photo.
He was 40 years old.
Diesel is the godfather of Meadow Walker and in November he turned 21 with a post on his Instagram account.
"I could say that I am very proud of the person you are becoming … but the truth is that I have always been proud of you. Happy birthday Meadow!" He wrote in the caption. "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 up. I love you, kid. Uncle Vin."