“Ahh! Congratulations to my brother… and sister in law to be on your engagement,” the “Remember I Told You” singer, 25, captioned a pic that the couple had posted earlier in the day showing off Turner’s shiny pear-shaped diamond engagement ring.
Big brother Kevin, 29, shared the same photo, writing, “Congrats @joejonas and @sophiet so happy to welcome you into the family!”
As Us Weekly previously reported, the couple, who began dating at the end of last year, announced their engagement on Instagram on Sunday.
A source told Us that the proposal happened today, adding, that Joe, 28, and the Game of Thrones star, 21, “are madly in love.”
“They are really good together and his friends and family love her and vice versa, but they aren’t rushing to get married,” the source added.
Kevin, Joe and Nick rose to fame as musical group the Jonas Brothers in 2008 after they starred in the Disney Channel movie Camp Rock and its sequel. They were nominated for a Grammy that year for Best New Artist and went on to sell more than 17 million albums worldwide before calling it quits in 2013, citing creative differences.
Nick went on to pursue a solo career as a singer and actor, with a recurring role on the TV series Smash, and released his third studio album, Last Year Was Complicated, in 2016.
Kevin and wife Danielle, who wed in 2009, starred in their own E! reality series, Married to Jonas, in 2012 and have two daughters, Alena, 3, and Valentina, 11 months.
Joe formed a new band DNCE, who had a worldwide hit with their 2015 debut single, “Cake by the Ocean.”