After Rob Kardashian and Blac Chyna announced their engagement to the world earlier this week, Tyga was one of the first to respond with well wishes to the couple.
"Everybody deserves 2 be happy," he wrote on Twitter.
"What some1 does for their happiness is not my concern, as long as it's not interfering wit my happiness."
"It makes me happy to see the mother of my son happy," added Tyga, who shares a three-year-old son, King Cairo, with Blac.
Sweet, right? Not in the eyes of his girlfriend ...
This simple note of congratulations royally ticked off Kylie Jenner, who has disapproved of her brother's relationship with her nemesis since it began in January.
Tyga and Kylie reportedly got into a huge blowout and broke up just before he left on his world tour Friday.
“All this drama really started when Tyga spoke out on social media about Blac and Rob’s engagement while she was away," a source tells Radar Online.
"Kylie had specifically told him to NOT say anything about it until she did.”
“Tyga talked so much sh*t about Blac being with Rob to Kylie behind Blac’s back and to everyone else and then he goes and sends them well-wishes."
"It just really p*ssed her off!” the source added.
However, while Kylie is busy fuming over Tyga's tweet, the "Rack City" rapper may have had an ulterior motive behind sending the message.
Blac believes her baby daddy is simply pretending to be civil so as to gain the favor of the courts in their custody battle over King.
In reality, says Blac, Tyga treats her like crap and has called her a "drunk whore" and a "deadbeat mama."
None of this matters to Kylie, however, who simply feels betrayed.
So far, Kylie has remained tight-lipped about her brother's engagement.