The Queen has wished Prince William happy birthday (Image: UK Press via Getty Images)

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The Queen has wished her grandson Prince William happy birthday in a touching tweet.

The Duke of Cambridge turns 39 today and wife Kate is likely to "pull out all the stops" to make his big day extra special, according to a royal expert.

His grandmother was one of the first to wish him a happy birthday today, tweeting: "Wishing The Duke of Cambridge a very Happy Birthday today! #HappyBirthdayHRH."

The Queen also shared four pictures of William either on his own or next to his wife and children.

It comes after Royal expert Katie Nicholl said she thought Kate Middleton would do everything she could to make sure her husband enjoys his special day after enduring a difficult period due to his rift with Prince Harry and the loss of their grandfather Prince Philip in April.

The author predicts Kate and William will spend the day at Kensington Palace with their children Prince George, seven, Princess Charlotte, six, and Prince Louis, three.

The Duke of Cambridge is now in the final year of his 30s

Ms Nicholl told OK Magazine: "Kate always makes birthdays and celebrations special for William and the children.

"She's very much like her mother Carole in that respect. She'll be aware that this year has been tough for William and will want both his birthday and Father's Day to be special for him."

She added: "Kate keeps William very grounded and she likes to show how important he is to her and the children.

"Especially after everything they've been through this year. It's only brought them closer."

According to Ms Nicholl, the Duchess of Cambridge will bake a cake to celebrate her husband's birthday and their children will make homemade cards and gifts.

The Queen shared four pictures of Prince William alongside the touching birthday message

It comes after Kate announced the launch of a centre for early childhood development.

The Duchess of Cambridge, who hopes to help generations of kids by giving them the best start to life, wants the issue to be treated as seriously as climate change.

In a video to mark the launch of the Royal Foundation Centre for Early Childhood, Kate, 39, said: “[The aim is] to raise awareness of why the first five years of life are so important for our future life outcomes.”

She added that she hopes to help create a “happier, more mentally healthy, more nurturing society”.