Great Britain's world-title winning men's coxless four has been broken up at the start of a season that culminates with the London Olympics.
The squad for the three 2012 World Cup regattas was named on Wednesday.
Pete Reed and Andy Triggs Hodge move into the four alongside Alex Gregory, with the final seat still to be decided between Tom James and Alex Partridge.
Greg Searle, 40, is selected in the eight, two years after the 1992 Olympic champion came out of retirement.
Richard and Peter Chambers have been selected into the lightweight men's four to race with Rob Williams and Chris Bartley, with the possibility that they could become the first siblings since Greg and Jonny Searle on the same Olympic team.
Heavyweight men's coach Jurgen Grobler is aiming for a fourth straight gold in the coxless four, made famous by the likes of Sir Steve Redgrave and Sir Matthew Pinsent.
Reed and Andy Triggs Hodge were part of the four that won gold in Beijing but have since been competing as a pair, although 14 successive defeats by New Zealanders Hamish Bond and Eric Murray had led to their move back to the four being widely expected.
Gregory retains his place in the four, with James - a Beijing gold medallist alongside Reed and Hodge - still in the running, but fellow world champions Ric Egington and Matt Langridge join the eight along with 20-year-old Constantine Louloudis at stroke.
"The last few months have been really tough in getting to this point," Gregory told BBC Radio Berkshire. "It's a big relief to be at this point and now we can concentrate on the task in hand.
"Andy and Pete coming into the four from the pair is a great thing. They are phenomenal athletes and really strong and powerful and row technically well, and I think I can fit in really well with them.
"The fourth person isn't decided but whoever that's going to be is going to make us even stronger and I am very confident we are going to have a good boat."
A young team of George Nash and Will Satch will replace Reed and Hodge in the pair for Belgrade, with an eye on developing them for the 2016 Games in Rio.
"It was a tough time to select the guys and put them in the right place," Grobler told the BBC.
"It was a tough decision because we never had so strong athletes as we had in the last three years. There are three guys from last year's silver medal eight not in the boat, so you can already see the level of selection we had to make in the last three weeks."
The World Cup involves three regattas, starting with Belgrade next month and moving on to Lucerne and Munich, with the squad named on Wednesday likely to be very close to the Olympic selection on 6 June.
Paul Thompson, coach of the women and lightweights, confirmed that two of Britain's best London medal hopes will compete in the World Cup, with world champions Katherine Grainger and Anna Watkins, and Olympic champions Mark Hunter and Zac Purchase, going in the double sculls.
"It's really nice to get the official nod for selection, we've been working for years towards winning London Olympic gold and it is nice to now focus on the race rather than all the hoops you have to jump through to win selection," Purchase told the BBC.
"Obviously Mark (Hunter) and I are a well-grounded crew and it is nice to focus on the goal.
"Having previous results behind us does nothing but support our cause and makes it a lot easier to go out there and win another Olympic gold medal."
World silver medallists Helen Glover and Heather Stanning will contest the women's pair.
"World Cups are important competitions in their own right but this one will be more significant than usual as it gives us the first glimpse of the potential 2012 racing form of our crews", said GB Rowing Team performance director David Tanner.
"We are always ambitious to do well and will want to see a number of crews on the Belgrade podium. We will take into account performances in Belgrade as we shape the team for the remainder of the season."