Jenelle Evans
is getting hitched!

The "Teen Mom 2" star revealed she and sometimes-boyfriend Gary Head are engaged this morning on Twitter -- posting a photo of the ring and the message "I'm the luckiest girl in the world to have @gary_head in my life."

Not many details have been released from the heavy tweeter yet, though Jenelle did reply to a follower who asked if Head got the rock from a gumball machine -- saying "no he def didn't."

And what does Jenelle's mother Barbara think of her new fiance? Well, according to the 21-year-old, mama "loves him."

The engagement comes as a bit of a surprise, considering Evans was back with her bad boy ex Kieffer Delp when she had her boob job earlier this month.