Robert, who starred as manager Jimmy Rabbitte in the much-loved film, is rumoured to have initially auditioned to play lead singer Deco Cuffe, eventually played by Andrew Strong.
Our world exclusive pictures show Robert and several of the cast paying a touching tribute to Alan Parker, the late director of one of Ireland's most favourite movies.
Among others from the cast who joined Robert to re-enact the famous 'Heroin Kills' concert from the flick at a special memorial bash for Parker in London last weekend, were Angeline Ball (Imelda Quirke), Bronagh Gallagher (Bernie McGloughlin), Ken McCluskey (bassist Derek Scully) and Michael Ahern (keyboard player Stephen Clifford).
We can also reveal that Andrea Corr - who played Jimmy Rabbitte's youngster sister Sharon in the hit 1991 picture - also took part in the event at the Savoy theatre and performed a song from Evita.
She starred as Juan Peron's mistress in the 1996 movie, which was directed by Parker and featured Madonna in the lead role of Eva Peron.
At the London gig, Colm Meaney, who played Jimmy Rabbitte snr, read out a tribute from Roddy Doyle, who wrote the book, published in 1987.
Among those who attended the star-studded bash, organised by Parker's widow Lisa Moran, were actress Emily Watson and film directors David Puttnam and Stephen Frears. Parker, who also directed Midnight Express, Mississippi Burning, Fame, Angel Heart and Angela's Ashes, died in London last July at the age of 76 after a lengthy illness.
Robert (52) started his career in a band called Housebroken and became a household name at the age of 21, as Jimmy. He works as music composer for commercials and artistic projects.
His most memorable line from the film was: "The Irish are the blacks of Europe, Dubliners are the blacks of Ireland and the northsiders are the blacks of Dublin ... so say it loud - I'm black and I'm proud!"
He tells the Sunday World about the Parker tribute. "We barely got time to rehearse," he says. "We had one rehearsal here and on the day it was just production.
"We did five songs, I did three. I was also playing bass. Angeline and Bronagh did one each and we had Ken and Michael, as well as a backing band, including Conor Brady and Ronan Dooney, who played guitar and sax on the soundtrack."
Although Robert did not get to sing in the film he did perform two songs on the soundtrack, Treat Her Right (which features on the opening credits of the film) and Slip Away.
"Nobody was expecting us to play," he recalls of last weekend's event. "We were in the gods for most of the gig and then came down secretly - all of a sudden the curtain went up and there we were.
"There was some footage from the DVD shown, where there was a bet between him (Parker) and me about getting on the soundtrack, even though I wasn't in the band in the film.
"It went down really well. There were lots of Lords and Sirs there. There were a lot of tributes from friends, producers he had worked with down through the years."
But what about previous reports that he originally auditioned for the role of Deco Cuffe. "I don't know if that's strictly true," he reflects. "There was one point when my band Housebroken were in the Factory (the Dublin studio used for auditions). I don't think I ever sang Mustang Sally.
"I think Andrew happened to show up in the studio and cover for his dad (Rob Strong) on some songs in the rehearsals, and that changed everything.
"They saw him and said 'OK!' And they knew because of his voice he was going to be the singer. They then had to pick the band and figure things out.
"I remember him (Parker) in his hotel, in Jury's, the night before he made the decision, with all the pictures of us on the ground and he was swapping them around. So, it was last minute."
He last saw Parker in Dublin around 2005 when the director and several of the cast did a photoshoot for Vanity Fair for a theme about music in films.
Despite his groundbreaking role in The Commitments Robert avoided the limelight and at the age of 25 became a lone parent to his son Milo and devoted his time to raising him rather than pursue a career in acting.
"I guess we just have to think of it that way, fate. A lot of people are in it for themselves. If you have that gene, the acting bug, I guess after a while you learn you have to push yourself," he says.
Robert, originally from Drumcondra, north Dublin, now also has a young daughter Aoise from a different relationship and is living with his wife Vanessa near Dublin city centre.
Earlier in the week he attended a dedication ceremony in Dublin for actor Johnny Murphy, who played 'Joey the Lips' Fagan in the film and who died in 2016 at the age of 72.
President Michael D Higgins unveiled a memorial bench for the late actor in Drimnagh.
"It's really funny because Colm (Meaney) and Patrick Bergin were there with the President and I kept on being pushed to get into the picture by photographers and reluctantly did, and then the locals realised it was me (from the film) and started screaming," he laughs.