They didn't attend the April 29 nuptials, but the Obamas will have the chance to congratulate the royal newlyweds in person.
The US President and his wife are set to meet the new Duke and Duchess of Cambridge – who have just returned from their honeymoon in the Seychelles – on their three-day state visit to Britain.
The US leader – who declared the UK-US partnership "an essential relationship for us and for the world" ahead of the state visit - arrived in the UK with the first lady one day earlier than planned to avoid the volcanic ash cloud.
Ensuring the VIP couple receive a royal welcome on their trip, the Prince of Wales and the Duchess of Cornwall will greet them at Winfield House, the residence of the US ambassador, before escorting them to Buckingham Palace.
There, they will be given a full ceremonial welcome in the garden by the Queen and the Duke of Edinburgh, before serving as guests of honour at a state banquet in the Palace ballroom.
The safety measures, the cost of which amounts to around £10million, have surpassed any security operation London has ever seen.
On any official visit, the statesman comes with his own vast security team and equipment to keep him safe.
But extra caution has been taken for his current trip, following the death of Osama bin Laden in a US raid in Pakistan earlier this month.
The president's bomb-proof Cadillac, nicknamed "The Beast", boasts eight-inch thick armour-plating on the doors, bullet proof glass, a GPS tracker and a panic button.
The vehicle is even said to carry his blood, with his private doctor travelling behind in case of an emergency.
An entourage of around 20 cars and a dozen police outriders on motorcycles will surround the vehicle as it moves through the capital.
The Obamas flew in from Ireland where they charmed thousands, greeting as many well-wishers as possible. In a speech in Dublin, he even uttered several words of Gaelic to the cheering crowd.
All the news as Duchess Kate's due date draws close...