Kate looked effortlessly chic in a bright blue knee-length dress which she matched with her favourite navy blazer and a blue velvet clutch. The electric blue Stella McCartney number was Kate's outfit choice just a few weeks ago at the opening of a new exhibition at the National Portrait Gallery
Kate and William avidly watched on with tense expressions as Murray suffered a slight wobble in the fourth game when he double-faulted twice, but held and then broke his opponent again in the following game with a brilliant forehand.
The Scot held superbly before breaking the Spaniard again in the seventh game to seal a victory that was greeted by a standing ovation from the crowd, including the Royal couple.
Despite the crowd's enthusiasm for the British number one's Olympics bid, there were still rows of empty seats in the stands, particularly in the lower tiers.
Hundreds of fans visiting the All England Club without tickets to the match gathered outside the court on Murray Mound to watch the action on the big screen as the sun shone down.
Murray was delighted with the quickfire victory in front of William and Kate.
He said: 'I didn't speak to them after the match but it's always nice when you're playing in front of royalty.
'When you get people like that coming along it helps raise the profile of the sport.
'It was a good performance today. I served well and that helped. It was good to get it finished early. I didn't want a long match because I am playing in the doubles this afternoon. Now I hope I can get a medal.'
Murray was disappointed to see rows of empty seats on Court One, however, and urged organisers to make sure the stands are full for his semi-final, and Sunday's medal matches.
'I would like to see all the seats full in all of the stadium but for whatever reason they haven't been,' the Scot said.
'The support inside and outside the stadiums has been great so hopefully over the weekend we will get all the courts packed.
'Centre Court was really busy the last two rounds I have played on there and hopefully they will all be full. Everyone wants to see that.
'Lots of people want to see the Games, there are lots of people trying to get tickets and it's not easy so I don't want to see any empty seats.'
The young Royals both looked effortlessly smart in the Royal box today as they cheered Andy Murray on to victory. William was once again spotted sporting his Team GB pin
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