Country music star Shelton also shared the same photo on his Instagram.
"Hey @gwenstefani thanks for saving my 2020… And the rest of my life.. I love you. I heard a YES!" the singer wrote in his caption.
"AMAZING! Congratulations to you both," fellow The Voice judge John Legend commented on Stefani's post.
"THE BEST!" singer and fellow coach Kelly Clarkson added.
*I guess our little interview aged well!!!!!! Congratulations!!! Best news," Dua Lipa added, referring to an interview from August this year, when she accidentally called Blake Gwen's husband.
"So I heard that you've been spending quarantine with your husband Blake Shelton at the ranch in Oklahoma. Who else was with you? How was that?" the New Rules singer had asked.
Gwen corrected her politely, stating that Shelton wasn't her husband yet.
"But that sounded cool when you said it," the former No Doubt frontwoman said.
She went on to describe their quarantine, revealing that they were actually on Shelton's tour when the country was shut down due to the COVID-19 pandemic. Stefani's brother was out with the couple, and Shelton's family soon joined.
"So it was me, my three boys, Blake, and then my brother, his wife, their two little babies, kids, and then her sister and then a friend," the singer recalled.
The musical pair have been together since 2015 when they met as judges on the set of reality competition show The Voice. Their friendship soon blossomed into romance, since the two had both recently left long-term public relationships.
Gwen, 51, was previously married to the musician Gavin Rossdale. They had three sons together – Kingston, Apollo and Zuma.
In 2016 the two artists went through a contentious divorce.
Blake, 44, was previously married to Kaynette Gern until 2006. He later tied the knot with music star Miranda Lambert before their eventual divorce in 2015.
The singers have collaborated on music together throughout their relationship. Shelton's track "Turnin' Me On" is reportedly about Stefani, and Stefani's 2016 song, "Make Me Love You" was written about Shelton, per CNN.
They have performed together multiple times and sang on the duets "Go Ahead and Break My Heart," (off of Shelton's 2016 album), "If I'm Honest" and "You Make It Feel Like Christmas" together.
Stefani and Blake had a lot to celebrate over this past week, since they also won a CMT Award for Best Collaborative Video for their country duet "Nobody But You", as The Inquisitr reported.
In an acceptance video recorded in their home, the pair told each other "I love you" and shared a drink together to toast their win.
"This is a crazy pairing in lots of different ways, but it's working!" Shelton added as he gestured between himself and Stefani. She laughed and thanked the fans.