The post swiftly racked up almost 80,000 likes and tens of comments, with one user writing: "Thanks for being so accepting of a same sex relationship. That is a wonderful quality to have, Robert."
Another said: "Congratulations to your friends! Love is love and this is truly beautiful."
The first photo in the series shows Robert laughing at a table with his friends, and the sweet moment drew a telling remark from the wildlife conservationist's rumoured girlfriend, Emmy Perry.
Emmy, a 14-year-old California born child actress, wrote beneath the shot, "You can feel the happiness in these shots", ending her comment with a black love heart.
Robert and Emmy first sparked romance rumours when they walked the red carpet together at a gala dinner in memory of Steve Irwin in Beverly Hills on May 6.
Emmy, who has appeared in hit US TV series Glee, is an animal advocate and founder of Emmy's Hope, an animal rescue charity.
If the whispers are true, the teenagers make a remarkably talented pair.
Robert recently showcased a preview of the second season of his family's reality show Crikey! It's the Irwins, a programme which follows mum Terri, Robert, Bindi and her longterm boyfriend Chandler Powell as they work with wildlife and conservation teams around the world.
Recently, Robert was also nominated for a photography award.
Watch this video to see the budding artist receive his nod!