Jay Rodriguez's solitary goal proved the difference on Sunday as United fell to a disappointing home defeat at the hands of West Bromwich Albion.
City were crowned champions thanks to the result, having missed out on the title the previous week when the Red Devils prevailed at the Etihad Stadium.
And United fans were in no mood to be gracious runners up when the club extended its courtesies to the Citizens.
"Congratulations to Manchester City on their Premier League title win," read the message on United's Twitter account.
Congratulations to Manchester City on their Premier League title win.— Manchester United (@ManUtd) April 15, 2018
The post was answered by widespread calls to delete, although a handful of Red Devils joined the club in sending their congratulations across the Manchester divide.
Delete this— Sam (@JuanderfuI) April 15, 2018
Delete right now— . (@Minimummensah) April 15, 2018
delete— Sur le front un M (@krissmoha) April 15, 2018
delete before people see— jackjwaugh (@jackjwaugh) April 15, 2018
The state of this! Delete..— Callum Maguire (@callummaguire96) April 15, 2018
Delete this. My heart can't take so much at once.— R™ 🇾🇪 (@RealTalkMUFC) April 15, 2018
Will United be able to topple their rivals next season and win back bragging rights in the city?