Dating since December 2011, the couple got engaged in New Orleans after Bass proposed to the aspiring actor and model with a black diamond band. He even texted his future husband's parents to ask for their permission first.
"They're such a great couple, everyone is so happy for them," another source tells Us. "Their friends and family are thrilled."
Turchin hinted at the engagement on Saturday, Aug. 31. "Happiest guy in the world," he tweeted.
Bass, 34, recently reunited with his *NSYNC bandmates to perform at the 2013 MTV VMAs since 2003, marking a very special moment for the singer in more ways than one. "For the first time ever I got to perform w *NSYNC as an out entertainer and was thinking of this man," Bass tweeted on Aug. 28.
Bass previously dated Amazing Race winner Reichen Lehmkuhlin in early 2006 and was briefly linked to Brazilian model Pedro Andrade in 2007. He dated New York-based hairdresser Ben Thigpen from August 2007 to March 2008. Bass publicly came out as gay in July 2006.
Lance posted this photo of himself with Michael on Sept. 1, 2013, with the caption, "He said YES!! Love this man."
Click on for more photos of the happy couple throughout their relationship...