The Pirates of The Carribean star and Moss split in 1998 after dating for four years, but they got together again when they were both invited to appear in The Beatles legend's promo for his new song Queenie Eye.
It will be the first time the former couple appears on screen together since the split.
A source tells Britain's Daily Record, "There were a whole host of celebrities taking part. It was a really mixed bunch. Meryl Streep and Gary Barlow were in the studio and there was an audience on set. But the big talking point was Kate and Johnny.
"They try to avoid one another in public as there have been raw emotions in the past, but neither could say no to MACca. They only have little roles, but it's the first time they're appearing on screen together since their split."