The 18-year-old Australian conservationist and former "Dancing with the Stars" contestant shared a new photo with Powell this week and gushed about the 20-year-old U.S. wakeboarder in the caption.
"Sometimes in life, you find that someone who is living Sunshine," she wrote on Instagram.
Irwin, who hails from Australia, and Powell, who lives outside Tampa, Fla., first met in 2013.
The conservationist previously called Powell her "sunshine" in December following a visit with the wakeboarder.
"I've known you since you were 16 and every day, from the very first day I met you, you've been my sunshine," she said in a post.
"Thank you for everything, you always make me smile, no matter how far apart we may be," the star added. "You really do mean the world to me."
Irwin is the daughter of late Crocodile Hunter Steve Irwin, and lives with mom Terri Irwin and brother Robert Irwin at the Australia Zoo in Beerwah.
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She and Powell have a long-distance relationship, but reunited in March.
"We talk every day and are together every two to three months," the star told People in 2015. "Thankfully I've found someone who is an outdoors kind of person. We'll go have adventures or picnic in the park."
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