Kate Middleton attended the RAF celebration despite being on maternity leave.

The Duchess of Cambridge stepped out on Tuesday to join Prince William, Prince Harry, Meghan Markle, Queen Elizabeth II, Camilla Parker-Bowles and more at the Royal Air Force's 100th-anniversary celebration. Initially, Middleton wasn't expected at the event, but she showed up.

According to Caitlyn Hitt, a journalist for Daily Mail, Middleton "felt the celebration was important to be at if she was feeling up to it." Middleton arrived in a blue Alexander McQueen coat with an RAF Dacre brooch.

This is not the first time that she breaks her maternity leave. In June, the royal mom of three joined the royal family at the Trooping the Colour, to celebrate the Queen's birthday. In May, she was also spotted at the Duke and Duchess of Sussex's royal wedding.

A day prior to the RAF celebration, Middleton and Prince William held Prince Louis' christening. The couple was spotted arriving at the Chapel Royal in St. James's Palace in London. The Duchess was holding Prince Louis in her arms. Meanwhile, Prince William held Prince George and Princess Charlotte's hands. It was the first time that the family of five was spotted together.

Also present at the event were Prince Harry, Meghan Markle, Camilla Parker Bowles and Prince Charles. Middleton's family including her parents Carole and Michael were there too. Her sister, Pippa Middleton was also in attendance with her husband, James Matthews.

Middleton has been on leave since April. In fact, she missed a few events. In May, she didn't attend Prince Charles' garden party where Markle made her debut as a royal.

Prince William and Middleton also didn't attend Celia McCorquodale and George Woodhouse's nuptials. The bride was the duke's cousin. Although they were not present, Prince Harry and Markle were there to represent the royals.

According to a royal expert, the Duchess of Cambridge may not return to her royal duties until October. However, she might make an appearance at some events.

"It is traditional for new royal mums to take a six-month break from official engagements," Duncan Larcombe told Harper's Bazaar. "The wedding doesn't count because it was a 'family affair' but other than that, she will pick and choose her engagements. If she wanted, Kate could disappear into the background until October!"

Royal Family
Why did Kate Middleton breaks maternity leave for RAF celebration? Pictured: Camilla, Queen Elizabeth II, Meghan Markle, Prince Harry, Prince William and Middleton watch the RAF 100th anniversary flypast from the balcony of Buckingham Palace on July 10, 2018 in London. Getty Images/Paul Grover