Why Prince William won't be spending Catherine's birthday with her this year

On Wednesday 9th January, Catherine, Duchess of Cambridge, will be celebrating her 37th birthday.

But it seems that the mum-of-three won't be able to mark the occasion with her husband, Prince William, by her side.

After a relaxing Christmas spent in the Norfolk countryside, it will be back to business for the Duke of Cambridge on 9th January, as he undertakes his first official engagement of the year.

Kensington Palace announced recently that William will instead spend the day visiting London's Air Ambulance, "to recognise the work that their first responders carry out delivering life-saving treatment across London".

The Duke will be the first younger member of the royal family to return to his official duties after the Christmas break, which he spent between the Queen's Sandringham Estate home and his and Catherine's country house, Anmer Hall.

The Cambridge's country home, Anmer Hall, in Norfolk

Although the engagement means that the pair won't be able to spend much of Catherine's special day together, it will likely be an important visit for William.

The future King of course spent many years as a pilot in the East Anglia Air Ambulance service, and so will be able to relate to the work of the London service well.

Of course, with busy schedules of engagements and meetings, it's also not the first time the Duke and Duchess of Cambridge have spent an important milestone apart.

In 2013, the couple spent their second wedding anniversary away from each other, as Prince William had work commitments, while the Duchess of Cambridge was on an official visit to children's hospice Naomi House.

And the royal pair have regularly spent Valentine's Day separately because of various duties. The life of the future King and Queen we suppose!

As of yet no information has been released about how the Duchess of Cambridge will spend her 37th birthday, but with three children to look after - Prince George, Princess Charlotte and Prince Louis - and two of them returning to school and nursery very soon, we're sure it'll be a busy day for Catherine!

Plus, we're sure that William and Catherine will be able to spend the evening together, perhaps for a special dinner.

It's likely that if they haven't already, Catherine, William and their family will return to their Kensington Palace home very soon, where they are based for most of the year.