Prince William and Prince Harry opened up about working together.

Prince William, Kate Middleton, Prince Harry and Meghan Markle graced the stage together for the first time. The fab four attended their first royal engagement together to take part in the first annual Royal Foundation Forum on Wednesday.

During the event, Markle's fiancé and Middleton's husband talked about their working relationship. Prince Harry and Prince William admitted that there were times when they disagreed too.

"Oh yes," Prince William said (via Express) when asked if they ever had disagreements while working together. "Healthy disagreements," Prince Harry added.

According to Prince Harry, their disagreements came along "thick and fast" that they could not keep track of it.

"The fact everyone is laughing means you know exactly (what I mean) - but we're stuck together for the rest of our lives," Prince Harry continued. "It does have its challenges. We're stuck together forever now."

Although there are disagreements, the Duke of Cambridge believes that they are stronger while they work together. "When we work together, we are greater than the sum of our parts," Prince William said.

Prince William also gave Prince Harry's fiancée a warm welcome. According to the Duke, he was "particularly happy at our first Royal Foundation event with Meghan."

The Duchess of Cambridge also showed her support to her future sister-in-law when she turned to Markle and gave her a round of applause.

Prince William, Middleton, Prince Harry and Markle were first seen together on Dec. 25. The fab four were photographed together while they walked their way to attend the royal family's traditional morning church service. The royal fans were very pleased to see them all together.

However, Markle's brown hat received an intense backlash from her critics. A number compared the "Suits" star's headgear into a rude emoji. Meanwhile, others compared it to a chocolate. In general, many find it as a fashion faux pas.

Meanwhile, on the same outing, Prince William showed a rare PDA when they held each other's hands as they walked their way to the church. The Duke and Duchess of Cambridge rarely touch each other in the public, so their sweet gesture did not go unnoticed to their fans.