"But it's hard to believe he went from not wanting to get married at all to a straight-up proposal", the source added.
Earlier today, the model shared photos of herself and her father at the beach, tweeting, "Life is good :) Venice Beach!"
E! News confirmed in May that The Voice judge and Agdal were an item.
The pair were spotted playing a game of volleyball in their swimsuits while on vacation in Cabo San Lucas, Mexico, in late June.
However, at some point between then and now, Levine decided to reconcile with Prinsloo—for better or worse, until death do they part.
The Maroon 5 frontman's rep confirmed to E! News yesterday that he proposed to the 24-year-old over the weekend in Los Angeles.
The duo was first spotted together in June of last year, stealing a smooch while vacationing in Hawaii. The couple was headed to Kauai for a friend's wedding and were seen holding hands and chatting up pals together during pre-ceremony festivities.
And then they lived happily ever after.