The Keeping Up With The Kardashians star was seen at Los Angeles International Airport on Saturday, 24 May - the same day that Kim and Kanye married in Florence, Italy.
No official reason for Rob's absence has been unveiled but reports claim that he felt uncomfortable with all the attention and extravagance of his big sister's nuptials.
A source close to the family told People magazine he also skipped a rehearsal dinner as it just wasn't "his scene".
It's been claimed by TMZ that Rob was seen "in tears" as he arrived at Florence's airport to catch his flight back home.
However, sources have told Us Weekly that Rob caught his flight from Paris, France, where the whole family had been enjoying a week of pre-wedding celebrations.
On his arrival in LA, sock designer Rob kept his head down and didn't speak with photographers. He was dressed in head to toe black and hid his face behind a jumper as he spoke into his mobile phone.
Rob isn't the only member of the Kardashian-Jenner clan to miss the nuptials; Kim's step-brother Brody Jenner was also a no-show because he was doing a DJ set in Chicago.
Since jetting into Europe last week, Rob has kept a low profile - although he did hit out on Twitter about reports he was seeking help at 'fat camp' to shift his excess weight.
Rob tweeted: "To the blogs saying I went to fat camp or rehab. LOL. Then why am I still fat you fools? Y'all must have run out of real news."
He concluded: "First, I don't believe in rehab or therapy or anything of that sort, and second, I'm a grown man and will work on myself when I choose. I'm aware that I'm fat that def aint a surprise to me lol and my only therapy will be in the gym anyways had to say somethingggggggggg."
Kim and Kanye married at the 16th century Fort Belvedere in Florence on Saturday.
Guests at the star-studded ceremony included the rest of the Kardashian-Jenners: sisters Kourtney, Khloe, Kendall and Kylie, mum Kris, and step-dad Bruce, who walked Kim down the aisle.
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