On average, the time between a couple’s engagement and their wedding day is between 12 and 18 months, but for Prince Harry and Meghan Markle, that gap has been narrowed to just six months. So what’s the story behind their whirlwind engagement?

According to one royal expert, there’s a touching reason for it. Insider Katie Nicholl told Entertainment Tonight that Harry chose the date to ensure Prince Philip, who earlier this year retired from public life, would be able to attend.

“He’s incredibly close to his grandfather and, being 96, Harry thought it was a great thing to [have] the wedding sooner rather than later, so his grandfather could be there, fit and healthy,” she explained.

In a similar vein, Nicholl believes Harry also kept his grandparents in mind when choosing the venue, St George’s Chapel in Windsor Castle. “[Harry] wanted something close to home for the Duke of Edinburgh and the Queen,” she claims.

“And, we understand it's where Meghan first got to know the Queen ... she spent time with the Queen at Windsor, so I think [it’s] a special place to both of them.”

The question of whether or not the Queen and Prince Philip will attend the big day at all is still up in the air. Technically, as head of the Church of England, Her Majesty is not supposed to “endorse” a marriage to a divorcee. Because of this, she and Philip did not attend Prince Charles and Camilla’s 2005 wedding ceremony.