Kate Hudson has celebrated her son Ryder's 18th birthday with a touching social media post.

Kate Hudson paid tribute to her son Ryder on his 18th birthday

Kate Hudson paid tribute to her son Ryder on his 18th birthday

The 42-year-old actress shared a sweet tribute to her son on his milestone birthday with a montage of photos from his life, beginning with a snap from her pregnancy and ending with a recent selfie of the pair and also quipped that his life is "outta my hands" now.

Kate - who shares Ryder with her former husband Chris Robinson - wrote on Instagram: "And then he was 18.

"My heart is filled with love and excitement for your future. Ryder you incredible, unique, hilarious, loving human, I love you beyond. Happiest Birthday @mr.ryderrobinson PS Now your life is your responsibility and outta my hands! Good luck son!!! (sic)"

The 'Almost Famous' star recently revealed that Ryder loves to joke about the fitness videos she shares on social media.

Kate - who is also mother to son Bing, 10, and daughter Rani Rose, three, from her relationships with Matt Bellamy and Danny Fujikawa respectively - told chat show host Seth Meyers: "Just the fact that I Instagram all of my products, so he makes fun of that."

Kate - who is the daughter of Hollywood star Goldie Hawn - added: "I mean, he's also deeply funny. Ryder — I mean, he clearly is gonna probably follow in the footsteps of the family.

"And I would say he's probably the funniest in our family. So, this is like every day for me. Nobody makes me laugh like Ryder, and he just constantly makes fun of me."