Prince William has "made history" by appearing as a cover star on leading gay magazine Attitude.
The Duke of Cambridge said "no one should be bullied for their sexuality or any other reason" in an interview with the publication.
And the royal called on anyone who was being bullied not to put up with it.
"Speak to a trusted adult, a friend, a teacher, Childline, Diana Award or some other service and get the help you need.
"You should be proud of the person you are and you have nothing to be ashamed of."
Attitude editor Matthew Todd says: "During my time as editor of Attitude I have met parents whose child has taken or lost their life after being bullied for being LGBT+ or just perceived to be LGBT.
"I am very happy that the future King of the United Kingdom agrees this must stop and I would urge parents in particular to raise their voices in their communities to ensure that every school protects – really protects – all children."
The magazine, which went to press days before the Orlando shootings at a gay nightclub, said it send its "most heartfelt condolences to those affected by this atrocity".
Read the full interview with Prince William in the latest issue of Attitude out on Wednesday June 22.