It’s hard to picture with all the dummy names, but I believe it all comes down to the fact that you switched from a return flight (albeit a bit complex on the way back) to a one-way flight.

Return flights are very often sold at a discount compared to two one-way flights, provided some rules are met (usually having either a Saturday night between the outward and inbound flights, or minimum/maximum duration). This is part of the differentiation between flights for business (which airlines try to sell at higher prices) and the rest, on which airlines are OK to make discounts.

So once you remove the first flight, you no longer qualify for the return discount, and the price is much higher (it can be spectacular). Add to that change fees, and the fact they usually reprice the ticket at today’s prices, which are probably higher as the flights filled up since your original purchase, and you can indeed quickly get a very high price to pay.

One thing you may want to try, is seeing if you can cancel the original ticket without too many penalties/fees and rebook a return the other way around (BBB-wherever-AAA and return to BBB). You wouldn’t use the last flight but that wouldn’t matter much.

Not that depending on where CCC is (especially if it’s in the same “region” as AAA or BBB, “region” being specific to the airline and sometimes to the fare), and the exact details of the rest of the itinerary (cities, flights, fares…), there may be other ways of optimising this, but we lack info.

It’s hard to picture with all the dummy names, but I believe it all comes down to the fact that you switched from a return flight (albeit a bit complex on the way back) to a one-way flight.

Return flights are very often sold at a discount compared to two one-way flights, provided some rules are met (usually having either a Saturday night between the outward and inbound flights, or minimum/maximum duration). This is part of the differentiation between flights for business (which airlines try to sell at higher prices) and the rest, on which airlines are OK to make discounts.

So once you remove the first flight, you no longer qualify for the return discount, and the price is much higher (it can be spectacular). Add to that change fees, and the fact they usually reprice the ticket at today’s prices, which are probably higher as the flights filled up since your original purchase, and you can indeed quickly get a very high price to pay.

One thing you may want to try, is seeing if you can cancel the original ticket without too many penalties/fees and rebook a return the other way around (BBB-wherever-AAA and return to BBB). You wouldn’t use the last flight but that wouldn’t matter much.

Note that depending on where CCC is (especially if it’s in the same “region” as AAA or BBB, “region” being specific to the airline and sometimes to the fare), and the exact details of the rest of the itinerary (cities, flights, fares…), there may be other ways of optimising this, but we lack info.

As for the “are they all doing this?”, most traditional airlines do, as this is how they build their fares: very expensive base price (fully flexible), and heavy discounts based on a number of conditions or restrictions (return flight, week-end in the middle, minimum or maximum duration, minimum or maximum advance purchase, less flexibility for changes and cancellations, restricted routings, restricted stopovers, use in sequence, etc.).

Low-cost carriers usually have a very different model where each leg is sold and priced separately, so they (again, usually) don’t care about return flights, use in sequence, etc. But low-cost carriers are a lot less present on the transatlantic market, and they usually don’t handle connections, so they are not always an option.

It’s hard to picture with all the dummy names, but I believe it all comes down to the fact that you switched from a return flight (albeit a bit complex on the way back) to a one-way flight.

Return flights are very often sold at a discount compared to two one-way flights, provided some rules are met (usually having either a Saturday night between the outward and inbound flights, or minimum/maximum duration). This is part of the differentiation between flights for business (which airlines try to sell at higher prices) and the rest, on which airlines are OK to make discounts.

So once you remove the first flight, you no longer qualify for the return discount, and the price is much higher (it can be spectacular). Add to that change fees, and the fact they usually reprice the ticket at today’s prices, which are probably higher as the flights filled up since your original purchase, and you can indeed quickly get a very high price to pay.

One thing you may want to try, is seeing if you can cancel the original ticket without too many penalties/fees and rebook a return the other way around (BBB-wherever-AAA and return to BBB). You wouldn’t use the last flight but that wouldn’t matter much.

Not that depending on where CCC is, and the exact details of the rest of the itinerary (cities, flights, fares…), there may be other ways of optimising this.

It’s hard to picture with all the dummy names, but I believe it all comes down to the fact that you switched from a return flight (albeit a bit complex on the way back) to a one-way flight.

Return flights are very often sold at a discount compared to two one-way flights, provided some rules are met (usually having either a Saturday night between the outward and inbound flights, or minimum/maximum duration). This is part of the differentiation between flights for business (which airlines try to sell at higher prices) and the rest, on which airlines are OK to make discounts.

So once you remove the first flight, you no longer qualify for the return discount, and the price is much higher (it can be spectacular). Add to that change fees, and the fact they usually reprice the ticket at today’s prices, which are probably higher as the flights filled up since your original purchase, and you can indeed quickly get a very high price to pay.

One thing you may want to try, is seeing if you can cancel the original ticket without too many penalties/fees and rebook a return the other way around (BBB-wherever-AAA and return to BBB). You wouldn’t use the last flight but that wouldn’t matter much.

Not that depending on where CCC is (especially if it’s in the same “region” as AAA or BBB, “region” being specific to the airline and sometimes to the fare), and the exact details of the rest of the itinerary (cities, flights, fares…), there may be other ways of optimising this, but we lack info.