Sir David Attenborough, Sir Alex Ferguson and David Beckham are among the big names at Wimbledon to watch the men's semi finals from the royal box on Thursday.
Novak Djokovic will face Spaniard Roberto Bautista Agut on Centre Court at 1pm, followed by Roger Federer and Rafael Nadal.
Agut's Wimbledon success was so unexpected he even scheduled his stag do for this weekend.
Despite missing out on a trip to Ibiza, Agut said: "It feels better to be here in London."
Agut's fiance Ana Bodi Tortosa was seated in the crowd to watch the match.
After Djokovic's match against Agut, Roger Federer will face Rafael Nadal – the first time they have played one another at Wimbledon since the Spaniard won their five-set final in 2008.
Tickets for the action on Centre Court are retailing for up to £11,000 on resale sites like StubHub and Viagogo – compared to the £185 they would have cost in the public ballot.
Sir David's visit to Wimbledon coincides with the club's ambition to cut down on plastic waste.
They have introduced "eco champions" on site to help visitors recycle, while sponsor Evian is using the tournament to pilot its 100% recycled bottle.
Earlier this summer, Sir David spoke on the main stage at Glastonbury to hail the festival's ban on bottled water.
"That's more than a million bottles of water that have not been drunk by you," he said.
He declined to speak to the press at Wimbledon on Thursday morning.
Both Federer and Djokovic have revealed themselves to be nature lovers at this year's tournament.
Federer said he loved enjoying Wimbledon's floral arrangements during the first week, particularly the ivy coating centre court and court one.
"When we wander around the grounds, we get a bigger chance to enjoy them," he said.
"We see the gardeners working on them. Afterwards it's very much press room, locker room – you start to sort of not see them any more."
"I like flowers," he added.
Djokovic has been worrying about injured wildlife – nursing a baby bird he found in the garden of a rented house.
Sadly the fledgling passed away before he could get it to a vet.
The world number one told the Telegraph: "Unfortunately she didn't survive the night. She had so fatal injuries so it was a sad end."
Other big names in the royal box are Hugh Grant, comedian Michael McIntyre, acting power couple Damien Lewis and Helen McCrory, Jude Law, singer Leona Lewis and TV survival expert Bear Grylls.
The action got under way on Centre Court at 1pm.