Terri Irwin's emotional birthday tribute to her now teenage son Robert

Robert Irwin with Mum Terri and sister Bindi. Photo / Getty Images

Terri Irwin has shared a touching message with her now teenage son Robert Irwin as he celebrates his 13th birthday.

The mum-of-two took to Twitter to wish Robert a happy birthday saying her late husband Steve lives on in him.

While my heart aches that Steve isn't here for Robert's 13th birthday, each day I'm more aware that Steve lives on thru his incredible son. pic.twitter.com/jykUoxiogS

— Terri Irwin (@TerriIrwin) December 1, 2016

Bindi Irwin also took to Instagram, saying she was so proud of her brother.

View this post on Instagram

Happy Birthday to this amazing human being, my brother 💛 Today you turn 13 and I am so proud of you. This photo was taken many years ago, I still can't believe that today you're a teenager. Since the first day I met you, when you were born, I knew you were destined for great things. You inspire me every day. I love you. Ps. You now have Instagram! @robertirwinphotography

A post shared by Bindi Irwin (@bindisueirwin) on Nov 30, 2016 at 5:13pm PST

Bindi's American boyfriend Chandler Powell, who is a professional wakeboarder, also wished the youngest Irwin a happy birthday, showing the pair clearly get along.

View this post on Instagram

Happy birthday @robertirwinphotography 🐊 You're the best photographer I know and congratulations on joining the Instagram world! Have the best birthday, can't wait to celebrate with you @australiazoo! Thank you for all the awesome Zoo Tours.

A post shared by Chandler Powell (@chandlerpowell) on Nov 30, 2016 at 5:16pm PST

Robert, who is a keen photographer made his debut on Instagram saying he was excited to be celebrating his birthday, the start of his teen years.