That's exactly what happened to Telford amateur boxer, Joe Lockley, whose dream came true when he was chosen as Joshua's opponent in a just-released advert for betting giant William Hill.
Joe spend four days filming at Wembley arena for the one minute, black and white, promotional video, which sees him knocked out by the champion. Instead of going down to the canvas Joe is seen suspended in mid air as time stops for Joshua enabling to him celebrate before returning to the ring.
The director of the Bright Star Boxing Academy in Shifnal, Joe, 27, from Lawley, beat off hundreds of people who applied for the role as Joshua's opponent, without even knowing about the job.
"It was our boxing club secretary, Kat Stanworth, who applied on my behalf. I got a call saying I had been shortlisted and thought it was a prank so I hung up. When she explained it was real I had to ring back and apologise," he said.
Standing six foot seven tall and a heavyweight boxer, he certainly fitted the criteria.
In the shortlist trials just before Christmas Joe was up against a professional boxer and an actor and was amazed to have been chosen.
"I had done a little bit of acting and modelling so I guess I had a good mix of everything," he said.
The filming took place in February at Wembley and Joe said he was treated like a celebrity.
"When they asked where I was staying and I said I had slept on a friend's couch the night before the first day they immediately booked me a room - at the Hilton," he said.
"A posh car came to pick me up every morning, I had my own dressing room, we were fed and even had massages, it was brilliant."
After the first day of rehearsals with an Anthony Joshua 'body double' the man himself arrived for three days of filming which Joe admitted took a lot of core stamina and involved him being suspended in a harness.
"He was amazing and when we met in the ring he said 'I know that guy, I've met you before' which was incredible as it was five years ago at an event in Cannock. But he said it wasn't often that he met people the size that I am.
"Then before filming started he insists on three round with pads, teaching me and seeing how I box. And for the rest of the time when there was a break in filming he was teaching me bits, going through my strengths and even asking me where I thought he could improve!
"Since then I have used a move he showed me which led to me stopping my opponent."
Joe, who works for the sporting charity Energize, said Joshua had been every bit as amazing as he had hoped.
"I was really worried about meeting him as he is a hero of mine. But he was so humble and so interested in the club that we run as volunteers, which is all about helping vulnerable kids In fact he had said that when he is travelling between Telford and London he will call in one day.
"He said boxing had changed his life and was very interested in the kids we work with."
The champion has also invited Joe to go and spar with him in June and the team involved in the filming, Sport Promotions, has signed him up for future work.