LONDON, England -- Movie godfathers Robert De Niro and Al Pacino have finally been reunited on the big screen -- but De Niro regrets how long it has taken.

"I wish it had been sooner," he told me on the red carpet at London's Leicester Square just before the film's UK premiere, "It's not so easy to get projects going. I wish, though, in spite of that that I had been more personally proactive ... and hopefully we'll do another project sooner than 13 years." Watch video of De Niro at the "Righteous Kill" premiere above.

The last film they were seen in together was Michael Mann's 1995 LA crime saga "Heat." Their shared screen time is a climactic six minute scene in a diner, which, at the time was likened to "Ben Hur sitting down and acting with Spartacus," by the New York Times. This time, they are acting together in almost every scene.

After all this time, though, according to De Niro who was first on board for the project (which is why he gets top billing), the genesis of their reunion was pretty spontaneous. He simply suggested Pacino to director, John Avnet: "I said, 'What about Al?' and that's how it started."

Pacino for his part says: "I thought, 'This is an opportunity to work with Bob again, and I'll take it.'"

With two such big names in one film, you might expect a bit of rivalry. Pacino says maybe in the old days but not now: "Early on in our careers I think there had to be a little bit when we were younger but I think we've gone past that.

"My rivalry is with Dustin Hoffman -- and Brad Pitt!"

For more from the "Righteous Kill" red carpet and clips from the film watch or subscribe to the Screening Room podcast.

-- From CNN's Mairi Mackay

Labels: al pacino, righteous kill, robert de niro