By PEOPLE.COM/Stephanie Petit
Jan 05, 2019 @ 1:00 pm

Royal duty calls!

Kate Middleton is celebrating her 37th birthday on Wednesday, but she will be spending at least part of the day away from her husband. 

That’s because Prince William, 36, has a solo engagement: He will be visiting staff members of London’s Air Ambulance, which is celebrating its 30th anniversary this year. William is set to meet with the charity at the Royal London Hospital in Whitechapel, where he’ll join staff, patients and their families at a tea party marking the anniversary.

It’s not unusual for royals to make public outings on days that coincide with a family event. In November, Prince William and Kate (rocking an apron!) visited the homelessness charity Centrepoint just hours before getting glammed up for Prince Charles‘ 70th birthday bash at Buckingham Palace.

Samir Hussein

With the couple’s two eldest children – 5-year-old Prince George and 3-year-old Princess Charlotte – heading back to school next week following the Christmas break, Kate will likely spend most of the day with Prince Louis, 8 months. The family will likely all be together for a small celebration that evening.

The family was also together over the holiday, when they spent time at their Anmer Hall home. Kate even revealed to fans that George and Charlotte gave them a very early wake-up call on Christmas.

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When a well-wisher at their annual Christmas church outing asked the pair how early they got up, William replied, “This morning was about 5 a.m.” Kate smiled at the answer as the crowd moaned at the early time.

Another royal fan, Jill Lee, told reporters that Kate shared a similar story. “I said to Kate, ‘Were the children up early?’ and she said, ‘Very early, but it was lovely to see their faces,’ ” according to Hello!

This article originally appeared on People. For more stories like this, visit people.com.