Los Angeles, Dec 16 : Hollywood star Gary Oldman has shared why he'll always be grateful for the 'Harry Potter' films. The 'Slow Horses' star, who is father to sons Alfie, Gulliver, and Charlie and step-son William, explained that he was cast as Harry Potter's godfather Sirius Black after becoming a single father. Oldman divorced his ex-wife, Donya Fiorentino, in 2001. 'At 42 years old, I woke up divorced and I had custody of these boys and so that, in itself, was'" he said on 'The Drew Barrymore Show', reports Entertainment Weekly. "That was hard because there was a shift in the industry where a lot of productions were being (filmed in), it was Hungary, Budapest, Prague, Australia, you know, all of these places.' Barrymore then explained to the audience that filming locations had shifted around the globe due to 'tax reasons'. As a result, Oldman said he 'turned down a lot of work' in order to be with his children. 'Thank God for Harry Potter,' he told Drew Barrymore. 'I tell you, the two ' Batman and Harry Potter ' really they saved me, because it meant that I could do the least amount of work for the most amount of money and then be home with the kids.' As per Entertainment Weekly, Oldman, who is 27 years sober, made his debut as Sirius Black in 2004's 'Harry Potter and the Prisoner of Azkaban'. He would go on to reprise the role over the following two instalments before his character's tragic end in 2007's 'Harry Potter and the Order of the Phoenix'. The Oscar-winner also starred as Gotham City Police Department Commissioner Jim Gordon in Christopher Nolan's 'The Dark Knight' trilogy, a role for which he flew back and forth from Los Angeles 27 times so that he could be with his children during his off days. 'I'd fly in for a day, I'd do a shoot a day,' he said. 'To (Nolan's) credit, he stayed on schedule and I would go home for three days, come back for two, go home for a weekend, come back for one day' otherwise, I just felt they're being brought up by a nanny.' Oldman admitted that he decided to be more hands-on as a parent after being 'not there all the time' for his first son, Alfie. He added: 'I got the opportunity to have these other two kids and I thought, 'I can't. I've now been given a real gift to be the dad I imagined I could be with the first boy, Alfie, and so I've got a chance to repair this and switch it around''. He said that his 'biggest accomplishment' as a parent is that his children grew up to become 'nice people.' /IANS