"Thank you for showing me the infinite power of a mama’s love," Bindi wrote alongside a pic of her hugging Terri. "You are the real life Wonder Woman. I love you beyond description."
Terri retweeted the touching note and added one of her own.
"I will love you beyond forever," Terri, 56, wrote to her eldest child. "Daughter. Wife. Mother. I am so very proud of you."
Terri shares Bindi and 17-year-old Robert with her late husband, Steve Irwin, who died in 2006. Bindi recently became a mom herself, when she and her husband, Chandler Powell, welcomed a daughter named Grace in March.
When ET spoke to the Irwins in February, Terri said that her late husband would've been "over the moon" to become a grandpa.
"He would've been a good, good grandpa. Yeah, he really would've been," Bindi agreed. "I don't think we would've ever seen our daughter. He would've just whisked her away into the zoo and it would've been perfect."
In a tweet following Grace's arrival, Terri again shared how Steve would've felt about his growing family.
"Love is not a big enough word. My heart is so incredibly happy. And I know that Steve would be beyond proud," she wrote. "Grace is the next generation to continue his mission and message of conservation. She chose her parents wisely. Bindi and Chandler are already the best parents ever!"