Slash has sent birthday wishes to his son, Cash, who has turned 21.

The legendary guitarist and Guns N' Roses rocker took to Instagram during the early hours of Monday to wish his son, Cash Hudson, a happy birthday.

"Happy Birthday CashHudson! I can't believe you're 21 already! You're a magnificently brilliant human being, and I love you with all my might. Have a great birthday!" the musician wrote alongside a throwback image of himself and his son.

Slash shares Cash with his ex-wife, Perla Ferrar, to whom he was married from 2001 to 2018. The pair also share an older son, London Emilio Hudson, 22.

In a November 2010 interview with The Guardian, Slash touched on how he maintains a close relationship with his sons.

"Having children is still changing me," he shared at the time. "I'm the eternal teenager, so having my two boys is kind of like having a couple of buddies around."

Cash's milestone birthday comes after a difficult year as a parent for Slash, whose stepdaughter, Lucy-Bleu Knight, died "peacefully" at 25 years old in Los Angeles on 19 July last year.

The guitarist referred to her as an "incredibly talented artist, a passionate dreamer and a charming, lovable, sweet soul" in his memorial post.