The production on the Tv movie adaptation of Larry Kramer's play shut down for three months to allow Bomer time to transform himself into early Aids victim Felix Turner - and Roberts, who plays a no-nonsense doctor in the film, admits she was shocked by how much weight her co-star had lost when they returned to the set.
She says, "It was like the smaller he got, the quieter all of his energy became. That was heartbreaking, to see someone allowing this dimness to take over.
"I hideously ate full lunches right in front of him, and I would say, 'Does this bother you?' 'No'. And he'd pull out his little lunch of a lettuce leaf and four almonds and be sweet as can be while I was having my Blt (bacon, lettuce and tomato sandwich) with a side of Blt."