Alongside the images - which also included a shot of the happy couple and Bel's sparkling engagement ring - Douglas wrote, "Very, VERY happy! @belpowley (sic)."
Douglas was subsequently congratulated on his engagement by a number of his famous friends and followers, including Bel's "The Morning Show" co-star Reese Witherspoon, who commented, "Well this is happy news. Congrats!"
"Ahhh congrats!!!!" remarked Lily Collins, as singer Jessie Ware posted, "Awwwww mazel tov (sic)!!!! Xxx"
And the groom-to-be's "Noah and Great Expectations" co-star Ray Winstone wrote, "Congratulations to you both. Much love. The Winnies."
The Brits met and fell in love on the set of the movie "Mary Shelley" in 2016.
Bel Powley also showed off her new fiance and engagement ring on her own Instagram. "Football's coming home…and so is my husband," so she exclaimed on her caption.
Congratulatory messages also came from the likes of Poppy Delevingne, Jenna Coleman, Vanessa Bayer, Naomi Scott, Gemma Chan, Gugu Mbatha-Raw, Sam Claflin, Jack Whitehall, Sarah Gadon, Ashley Benson, Daisy Lowe, Alexa Chung, Dan Stevens, and Pixie Lott.