Ranger Mathiew Shamavu snapped this heartwarming shot of his upright but chill gorilla pals on Thursday, and by Saturday night, more than 17,000 had liked it.
Innocent Mburanumwe, deputy director of Virunga, told the BBC that that the gorillas' mothers were both killed in July 2007.
After the image began gaining widespread attention online, park officials took to Instagram to verify the photo and share more background on the sensational moment.
Primatologist Frans de Waal told The Washington Post that animals often mimic human caretakers. Primates are even more likely to do so, he said, because they have "similar bodies" that make it easier.
"Imitation is often driven by attachment."
The gorillas were just two and four months old at the time.
"Those gorilla gals are always acting cheeky so this was the ideal shot of their true personalities!" the post continued.
Because they've grown up with the rangers who rescued them, Mr Mburanumwe added, "they are imitating the humans" - and standing on two legs is their way of "learning to be human beings". "It is never permitted to approach a gorilla in the wild". They've resided at the Senkwekwe Centre for Gorilla Orphans since they were small, where they are cared for by many staff members.
"These local men and women go through intensive training, risking their lives on a daily basis to safeguard the park's exceptional wildlife, including the last of the world's critically endangered mountain gorillas", the website says.