Arnold Schwarzenegger and Maria Shriver may have split in 2011, but the two put on a united front when they attended their son's college graduation on Friday.

The pair, who had broken up over Schwarzenegger's affair with their housekeeper, reunited at the University of Southern California's commencement ceremony to support their son Patrick.

In a photograph posted on Instagram, any strife appeared to be water under the bridge, as the proud parents stood on each side of their son and offered words of encouragement.

Schwarzenegger wrote a touching tribute that read: 'Patrick, I'm so proud of you. You have grown into a great man - physically and mentally - and I can't wait to see what you do next. Congratulations. I love you.'

Arnold Schwarzenegger (right) and Maria Shriver (left) may have split in 2011, but the two put on a united front when they attended their son Patrick Schwarzenegger (center) college graduation on Friday

Schwarzenegger wrote a touching tribute that read: 'Patrick, I'm so proud of you. You have grown into a great man - physically and mentally - and I can't wait to see what you do next. Congratulations. I love you'

Shriver posted two pictures of the occasion on Instagram on Friday, writing: 'The one the only @patrickschwarzenegger graduated!! So proud of him. Love this pic. Onward'

Patrick, who previously dated Miley Cyrus, is taking after his father and building up his own acting chops by landing a role on the TV show Scream Queens.

He also thanked his father's kind words on Twitter, writing: 'Danke papa. Couldn’t of done it without yah.'

Shriver posted two pictures of the occasion on Instagram on Friday, writing: 'The one the only @patrickschwarzenegger graduated!! So proud of him. Love this pic. Onward'

Another caption the day after read: 'Off he goes. Well loved, well educated. Share pictures of your #graduates with me. It's such a emotional day. #graduationday'

Shriver and Arnold had four children - Katherine, Christina, Patrick and Christopher, over the course of their 25-year marriage.

The former bodybuilder admitted to having an affair with his housekeeper Mildred Baena, with whom he secretly fathered a son, Joseph.

Shriver and Schwarzenegger seem to be on good terms again after it was revealed the former California governor fathered a son with their housekeeper. They appeared together at former First Lady Nancy Reagan's funeral in March (pictured)

Shriver filed for divorce in 2011, but TMZ reported in October 2015 that Arnold had yet to sign the papers and finalize the divorce.

The two reportedly worked out the financial settlement ages ago, agreeing to split roughly $400 million between them.

It is not known why the star isn't ready to formally quit the marriage, as he has moved on with Heather Milligan, 40, whom he has been dating for almost three years.

In an 60 minutes interview in 2012, Schwarzenegger said: 'I think it was the stupidest thing I've done in the whole relationship. It was terrible. I inflicted tremendous pain on Maria and unbelievable pain on the kids.'

But the two seem to be on good terms again, and appeared together at former First Lady Nancy Reagan's funeral in March.

The former California Governor, 68, and his ex, 60, sat beside each other during the services and were seen keeping close under an umbrella as they walked to another one of the day's events.