Meghan Markle Attends the Queen's Staff Christmas Party — at Her Future Wedding Reception Venue!

Meghan Markle hit another major milestone in her journey to joining fiancé Prince Harry‘s family: her first royal Christmas party!

Meghan was a guest, alongside Harry, at the annual Christmas party for staff at Windsor Castle, PEOPLE has confirmed.

Queen Elizabeth, who was joined by her son Prince Andrew and some of her cousins, used the occasion to help welcome Meghan into the fold. And she was at east as she moved around the gathering, impressing the several hundred guests with her humble approach and friendly manner, according to party attendees.

The party was held in a set of rooms, including the Waterloo Chamber, St. George’s Hall and the Grand Reception Room — an area of the castle Meghan and Harry will become even more familiar with as they plan their wedding in May.

“The Christmas party is always held there. They’ll hold the wedding reception there, too. It is a well-proven system and arrangement,” a former staffer tells PEOPLE.

St. George's Hall
St. George's Hall

The news of the holiday party came as the palace announced Meghan will be joining the royal family at their Christmas festivities at the Queen’s country home, Sandringham — making her the first unmarried partner to be on the guest list.

Waterloo Chamber
Waterloo Chamber

Some insiders are surprised at how fast Harry and his fiancée are being received into the royal family and its traditions. But it is a sign of how keen the Queen is for her to get to know the palace staff members.

“These things happen, times move on,” says the former staffer, who adds that the Queen is much more relaxed about the the so-called rules then in the past, and likely wants to have an “easy life.” The source adds, “Harry certainly gets a lot more leeway than most have done.”

Meghan is reported to have told guests that she and Harry stayed at the castle over the weekend — the prince had just returned late Saturday evening from a hunting party in Germany. The couple chose St. George’s Chapel for their wedding venue because Windsor is a spot that is a “very special place for Prince Harry,” his spokesman has said. The couple has spent a lot of time there as their relationship has grown.

Buckingham Palace and Kensington Palace did not comment as it was a “private event.”