Oscar winner Brie Larson has poured her heart out about her young Room co-star.

The 28-year-old picked up gold for her role in the film at the Academy Awards last month (Feb16), but in a heartfelt new Instagram post, she insists the real prize was meeting and working with Jacob Tremblay, the child star who played her son in the movie.

As she wraps up months of promoting the film around the world, the actress has taken to Instagram to share a sweet message for her onscreen son.

"28 weeks ago (according to Instagram) @roomthemovie premiered at the #telluridefilmfestival," she wrote. "After the screening @jacobtremblay and I toasted. He had chocolate milk and I had red wine. I remember feeling so vulnerable after sharing this movie with the world for the first time; unsure of what was to come.

"Last night marked what may be our final toast to this film. He had a soda and I had sake. We are in Japan."

The pair has spent the past two years "hanging out" and "playfully arguing about things like who can hold their breath longer", and Brie admits she'll miss the little fellow now there are no more press junkets or red carpet events to attend.

"We were generous and patient with each other," she added. "We laughed a lot, especially when it was hard. We picked each other up, answered for the other when one was tired and always kept silliness alive."

Brie concluded her note by writing: "Thank you Room for bringing us together. Thank you Room for uniting us with the rest of the world. Thank you to everyone who shared this journey with us. I will never ever forget it."