The 19-year-old model and reality star posted the clip to Instagram, showing various never-before-seen outtakes from Keeping Up With The Kardashians featuring Rob laughing.
It's poignant because Rob's personal struggles have been well documented over the past year and he's rarely been seen in public for the last twelve months.
Kendall's caption for the video was: "This makes me ridiculously happy."
The only son of Kris Jenner has shied away from the limelight ever since he left sister Kim's wedding celebrations in Paris, France last year and flew home before the actual nuptials.
Since then, his family have spoken about him in interviews, suggesting he's unhappy with his weight gain and suffering from social anxiety. An episode of Keeping Up With The Kardashians earlier this year showed the family considering an intervention.
In an interview with the Today show in April, sister Kim said: "I think he's just going through a phase where he's not comfortable in his own skin. And he's working really hard to get back to where he wants to be.
"I think it's been circumstances in his life that he just really hasn't dealt with. Whether it's, you know, the loss of our father, or certain breakups, or, you know, he was extremely close to Lamar [Odom] and when, you know, Khloé and him broke up, that was really hard on him. So I think it was a couple things."
Sister Khloe, meanwhile, told Wonderwall: "I just feel, especially over the last year, Rob has become very introverted and has a kind of social anxiety. He's definitely not at his happiest place that he once was, and I know he can get to that happy place and he will."
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