What happened to the original crew of Apollo 13 and why were they bumped from the assignment?

The original crew of Apollo 13 consisted of Jim Lovell, Fred Haise, and Ken Mattingly. They were bumped from the assignment due to Mattingly being exposed to German measles, which posed a health risk in space. As a result, he was replaced by Jack Swigert, while Lovell and Haise remained on the mission. The Apollo 13 mission ultimately faced a critical failure, but the crew successfully returned to Earth.