Robert turned 13 on Wednesday
Credit: Newspix/Getty Images

Terri Irwin is saddened that her late husband Steve isn’t alive to see their son grow up — but she is at peace knowing the Crocodile Hunter’s spirit lives on.

On Wednesday, Terri took to Twitter to honor both Steve, who was killed by a stingray during a diving expedition off the coast of Australia in 2006, and their son Robert on his 13th birthday.

“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,” Terri, 52, tweeted with a throwback photo of her husband holding their son as an infant.

Bindi, now 18, also celebrated her brother’s birthday on social media with a heartfelt Instagram post. “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!”

And to mark the day he became a teenager, Robert joined the world of Instagram! “G’day everyone, it’s Robert Irwin here! I’m so excited, it’s my 13th birthday today, and I invite all of you to check out my Instagram page,” he said while holding two large cameras and a snake, which he brought close to his face at the end of the video.

The Crocodile Hunter’s family recently celebrated Steve Irwin Day at a zoo in Australia alongside some of his favorite reptiles. Donning khaki uniforms, a tribute to Steve’s signature look, the family educated spectators about reptiles. At the zoo, Robert held a young reptile in front of an audience at the zoo — and proved that he is the spitting image of his father.

In the 10 years since Terri said goodbye to her husband, the mother of two has not “been on a single date since Steve died.”

RELATED VIDEO: Bindi Irwin Posts Touching Tribute to Her Late Father Steve on Instagram

“If I hadn’t met Steve, I probably would never have married because I wasn’t looking for love when I met him,” Terri told The Australian Woman’s Weekly. “What we had was incredible.”

But although Terri is living life without her husband, she is “thankful” for the time she had with her lifelong love.

“Thankful. 14 years of adventure and two beautiful children,” Terri tweeted on Thanksgiving in addition to an old family photo. “Thank you to all @wildwarriors keeping Steve’s legacy alive. #Thanksgiving.”