Khloé took to Instagram on Monday to share a heartfelt message to her younger brother, posting a throwback photo of Rob kissing her on the head.
"If only you could see yourself through my eyes!" Khloé wrote. "I'll forever be obsessed with you! My one and only! #MyAce"
The message did spark a response from Rob, who retweeted his sister. "AWWWW this made me tear," he wrote.
See more about Khloé's recent weight loss:
Rob, 28, has struggled with depression and weight issues for the past two years. In an April episode of "Keeping Up With the Kardashians," his mother, Kris Jenner, said he gained 100 pounds in the last year.
"I've been working on my patience," Khloé, 31, told People in October about Rob. "I've been really trying. But I have my moments and I do snap. I've offered to get a chef, I'm like, 'What's your excuse?' But it's not just that. I can't win life for Rob. I have to wait until [he's] ready to do it for himself."
"Rob is such a great guy," she added. "He's charming, charismatic, everything. That's what's so infuriating. I'm like, 'Where is your will to live life? Let's be around people!'"
Rob currently lives with Khloé in her Calabasas, California, home and has been keeping a low profile from the public for more than a year. Earlier this month, Kris revealed that her only son didn't spend Thanksgiving with his famous family.
"He lives with Khloé [who hosted the holiday dinner this year], so he was around, and then went over to a buddy's house," Kris told Maria Menounos on her Sirius XM radio show, Conversations With Maria. "He's doing alright, he's doing his best. "He's working on himself."
"He's gonna be OK," she continued. "He's not as into being on camera as the rest of us."
Apparently, he's not that into social media either. Rob has been largely absent from both Twitter and Instagram this year, though he did take some time out last week to promote his younger sister Kylie Jenner's sold-out lip kit. Curiously, he made no mention of a much more significant event that happened in the Kardashian family, although the news broke the same day -- Kim Kardashian giving birth to her second child with husband Kanye West.
More from AOL.com:
Tina Fey says Colin Quinn called her C-word at 'Saturday Night Live'
When Teresa Giudice will leave prison and how she's celebrating the holidays
Tom Brady on backing Donald Trump: 'I support all of my friends'