The reality TV star gave out what Us Weekly can confirm is one of his youngest sibling’s actual digits, not once, but twice on his social media account.
“Kylie’s #….I ain’t hacked either this is rob dog lol,” he wrote after posting the number followed by 16 laughing-crying emojis.
The 29-year-old then tweeted the number — that is now disconnected — again, before revealing the reason for his spiteful move.
“Didn’t invite the Mother of my child to a baby shower you were trying to throw me !!? You all must have lost your damn mind.”
He was of course referring to his fiancée, Blac Chyna, who is expecting their first child in October.
This isn’t the first time he’s lashed out on social media. In July he deleted all trace of the pregnant model and their relationship from Instagram after they had a row.
Rob’s decision to spark up a relationship with Chyna was controversial, since she is the ex-girlfriend of the Lip Kit creator’s boyfriend, Tyga.
The former couple also have a 3-year-old son, King Cairo, together.
Lately, though, the Kardashian-Jenner clan appeared to have put their differences with Rob’s wife-to-be behind them.
In a recent episode of Rob & Chyna, it looked like they had warmed to her as she joined the family at Khloé Kardashian's birthday party.
Kylie, 19, has even posed for Snapchat pictures with her brother's fiancee and insisted they are “friends."
Rob & Chyna airs on E! Sundays at 9 p.m. ET.
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