Prince William turns the big 3-0 today.

And while reports say he's keeping the celebrations low-key -- with wife Princess Kate and a few close friends -- here at HuffPost Impact we'd like to mark this milestone in a champagne-bottle-popping kind of way, and take a look back at how this once trend-setting-teen royal has grown up into a benevolent prince, determined to help those in the most need.

SLIDESHOW:

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  • Health Causes

    Five years after taking on the role of president of the Royal Marsden Hospital -- a position once held by his late mother -- Prince William and his wife <a href="http://www.usmagazine.com/celebrity-news/news/prince-william-kate-middleton-attend-childrens-cancer-center-opening-2011299" target="_hplink">opened one of the largest comprehensive children's cancer centers in Europe</a>, <em>US Weekly</em> reports. The royal couple partook in the hospital's opening ceremonies in September and visited with the young cancer patients.

  • Animal Rights

    Black rhinos have become critically endangered because they're killed for their horns, and Prince William is determined to do something about it. <a href="http://www.bbc.co.uk/news/uk-18489579" target="_hplink">In an interview with the BBC</a>, the animal rights activist called the illegal practice "ignorant, selfish and utterly wrong" and said that "if we don't do something about them, it's going to be a tragic loss for everyone."

  • Homelessness

    To develop a real sense of the struggles homeless people face, Prince William -- who serves as patron for the charity <a href="http://www.centrepoint.org.uk/" target="_hplink">Centrepoint</a> -- slept on London's chilly streets one night in 2009, <a href="http://www.huffingtonpost.com/2009/12/22/prince-william-spends-nig_n_400381.html" target="_hplink">the AP reports</a>. "I hope that by deepening my understanding of the issue, I can help do my bit to help the most vulnerable on our streets," he told the news outlet.

  • Anti-Bullying Advocate

    Instead of gifts, Prince William and Kate <a href="http://www.huffingtonpost.com/2011/03/16/royal-wedding-charity-gifts_n_836429.html " target="_hplink">asked their wedding guests make a donation to one of 26 charities</a> they selected, which included <a href="http://www.beatbullying.org/" target="_hplink">Beatbullying</a>, a nonprofit that offers mentoring programs to young people in the U.K. affected by bullying.

  • Veterans Issues

    Because caring for veterans' well-being is a main focus of his <a href="http://www.princeofwales.gov.uk/newsandgallery/focus/the_foundation_of_prince_william_and_prince_harry_570302665.html" target="_hplink">foundation</a>, Prince William headed off to the U.S. to find out how to better address such pressing issues as veteran employment. While speaking at a hiring event in Los Angeles in July 2011, the benevolent royal remarked: <a href="http://www.huffingtonpost.com/2011/07/11/prince-william-military-families-_n_894312.html" target="_hplink">"We have much to learn from you. Thank you for this opportunity."</a>

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