The identical-looking brothers got the full red carpet treatment at the opening night of the film King Arthur and the Legend of the Sword in which they star as Young Arthur.
And among the stars joining them there was footballing legend David Beckham who makes his movie debut in the film which is due for general release on May 19.
Oliver and Zac - from Ashington - were picked for the role after Guy Ritchie spotted their acting talents in the television drama Downton Abbey in which they played George Crawley.
The boys are, in fact, triplets with sister Megan and the trio are all in Year 1 at Ashington CE School. But Megan has, so far, steered clear of the limelight.
Proud mum Clare explained how the youngsters’ latest role came about. “I had a call from the boys’ agent at the beginning of 2015 wanting Oliver and Zac to meet a casting director for a role in a major movie - in fact, he wanted to see all three triplets as they were also after a girl of similar age to play the cousin. So we took Megan along too - although she was extremely shy and didn’t want to do anything.
“It was during this meeting that we discovered that Guy Ritchie would be directing, and he had seen the boys on Downton Abbey. Shortly after that meeting, the boys were offered the role of Young Arthur.
“They were only four and a half when they started filming King Arthur. It was being shot at the same time as they were also filming the last series of Downton Abbey, so there were days when it was a bit of a juggle.
“The boys, and myself, had no idea what to expect but the crew were fantastic and talked us through each process.
“We had a day in London prior to filming for the boys to get measured for their costumes.Then the first day on set is when we discovered their main costume - a shawl, of sorts, made from beaver skin, and footwear made of reindeer hide. The boys found this quite funny.
“We had about 25 days filming in total from March - June 2015, which also included some night shoots.
“There are very strict rules on how long children can be on set; hence why identical children are often used at a young age.”
Oliver and Zac shot all their scenes at Leavesden Studios which is where the bulk of Harry Potter was also filmed.
Clare said: “We would be chauffeur-driven and put up in the Grove Hotel - an incredible 5 star hotel where we would get driven around on golf buggies and the kids made use of the ‘children’s pool’ and games room - definitely a nice taster of movie star life!
“Each time we were driven onto set, we drove past the Harry Potter triple-decker bus which the boys loved. It was pretty incredible as the studio had built a full size castle with lakes etc. The amount of work that went into making this all look so authentic was unbelievable.
“The boys had their own trailers both by the production area and another next to the main studio area. Everything they could’ve wanted was put on.
“There was a lovely coffee bar on set and the ladies would make the boys special hot chocolates - then one day a sweet bar appeared so there were also never ending treats.
“I was always asked what the boys would like to eat and the on-site caterers would make their food especially - normally just pasta or pizza.”
The boys met Guy Ritchie on their first day on set. “He was lovely,” said Clare. “We were also filming alongside many other big names - Eric Bana was their ‘movie Dad’, Poppy Delevingne was ‘movie Mum’ and Jude Law ‘movie Uncle’.”
And the family got a chance to rub shoulders with a host of other stars - including Djimon Hounsou and David Beckham in his first movie role.
“All of them were really lovely, and made a big fuss of both Oliver and Zac,” said Clare. “Guy Ritchie even wrote a congratulatory message on one of the call sheets to my brother and his wife who gave birth to twins on one of our filming days!
“None of this meant anything to the boys though - they just saw the whole experience as fun and were unfazed by it all.
“There was a scene which involved the boys having to have fake blood applied, which they found amusing; but the days when horses, sword fighting and boats were used were very memorable.
“There is also one scene where Young Arthur had to have his hair cut, but because we were also contracted to Downton Abbey, they couldn’t cut real hair, so a weave was put on Oliver and he had to do that scene with no brotherly back up.”
Clare took hundreds of photos from the filming so that the boys will have a record of their achievements when they grow up.
“The main cast members were all very obliging to having their photos taken with the boys - I’ve got a great one of Zac and Jude Law both with their fingers up their noses!”
Oliver, Zac and Megan were not at school during their time filming so no special arrangements had to be made for their tutoring. And now it seems that Megan may soon follow in her brothers’ footsteps.
“Megan loves the fact that her brothers have been on the TV and is very excited about watching the film,” said Clare.
“She has now started drama lessons which has boosted her confidence, although at the moment her aim is to become a doctor.
Clare and husband Damian have now purposefully limited the time the boys spend filming as “school is more important; but they do the occasional job in school holidays.”
But if a Downton Abbey movie is ever made “we’d definitely do that as it’s something the boys know - and it would be great to see everyone again.
“We do keep in touch with some of the cast and crew - especially Michelle Dockery and Hugh Bonneville; and we bumped into Laura Carmichael when the children did a day’s filming on the movie A United Kingdom.”
Meanwhile, the family saw a preview of King Arthur, Legend of the Sword on Sunday.
“I am still a little overwhelmed,” said Clare. “The film was amazing and I was completely taken aback as to how much screen time Oliver and Zac got!”