Arnold Schwarzenegger admits having a child with another woman has caused a ''very tough'' situation.

The 67-year-old actor, who separated from Maria Shriver - the mother of his kids Katherine, 25, Christina, 23, Patrick, 21, and 17-year-old Christopher - in 2011 after he confessed that he had fathered a son, Joseph, now 17, with their housekeeper Mildred Baena, has a ''fantastic'' family and they are all working together to ''figure out'' their dynamic.

He said: ''[My family is] fantastic, including my fifth child with Mildred.

''He's terrific and he totally understands the situation. So, it all has worked out ... It's a very tough situation for him. It's a very tough situation for my kids, very tough situation for my family. It was tough for everybody. But it has happened and now we have to figure it out, right?''

The former Governor of California is thankful his estranged wife has worked with him to ensure he still has a good relationship with their kids.

He said: ''It has worked out really so well with the help of Maria.

''My kids are a straight 10. I am so proud of them. I'm so in love with them.''

But the 'Terminator Genisys' actor admits his split from Maria is one of the ''biggest failures'' of his life.

He added in an interview with SiriusXM DJ Howard Stern: ''''I had personal setbacks, but this was, without any doubt, the biggest setback and the biggest failure.

''Without any doubt. Not only failure, but you feel like, 'I'm to blame for it. It was me that screwed up.' And you can't point the finger at anyone else. So yeah, I was disappointed in it. It's always easy to be smart in hindsight.''