Robert Downey Jr became an instant fan favourite when he first starred in 'Iron Man' and after a decade, amid the reports of him dropping the armour, director Joe Russo said no actor can replace the Hollywood star as Tony Stark.

There have been rumours that Downey Jr, who has played the iconic superhero in around 10 Marvel films, including the upcoming 'Avengers: Infinity War' and its sequel, will step down as Iron Man after the release of 'Infinity War'."

"There is nobody who can take over Iron Man from Robert. I don't think the audience would accept that. He never mentioned to us about leaving 'Iron Man', but it will happen at some point of time."

"He can't play the character forever. I am sure there are lots other things he wants to do in his career. But he loves playing the character, I know that, and we love working together. We will see where it goes from here," Joe, who has co-helmed the film with brother Anthony Russo, said in a group interview here.

'Infinity War' boasts of a towering cast and the filmmaker said, true to his on-screen avatar Iron Man, Downey Jr made sure everyone moved together like a unit throughout the filming process. "Robert is an incredible leader. He is a very warm and inclusive human being. He is great in keeping everyone's spirits high and making everyone feel invited in the process... In the healthy creative space," he added.

The film, scheduled to release on April 27, is being touted as the biggest Marvel movie ever. Joe said, for him, the project is a step towards a more diverse Marvel Cinematic Universe (MCU), latest example being Ryan Coogler-directed 'Black Panther'.

"For me, this Marvel Universe is like a book. It has been in writing for last 10 years with all these films. 'Infinity War' is the final chapter in this book. So, in future, there will be new stories to tell. In future, we will be seeing a new beginning. 'Black Panther' is one of them and it is so incredible. The future of Marvel is going to be a lot more diverse catering to fans across the globe."

"People have been (living) with these characters for a decade and this is the ending. It is very exciting as there is a sense of closure and then also of new beginnings," he said.

The film features an A-list cast - Benedict Cumberbatch, Karen Gillian, Chris Hemsworth, Mark Ruffalo, Chris Evans, Scarlett Johansson, Don Cheadle, Tom Holland, Chadwick Boseman, Paul Bettany, Elizabeth Olsen, Anthony Mackie, Sebastian Stan, Danai Gurira, Letitia Wright, Dave Bautista, Zoe Saldana, and Chris Pratt among others.

Joe said there were no differences on the sets and they worked like a team. "There were no ego clashes. We were like a big happy family," he added.