Edan Alexander was kept hostage underground for 583 days in the tunnels beneath Gaza. After he was released on Monday evening, he stood in a plain white room on an Israeli military base as his mother rushed in. They hugged and cried with joy and wept.

Adi Alexander, Edan’s father, wanted to join their embrace. Instead he waited down the hall. For more than a year and a half, Mr. Alexander had relied on discipline to survive the ordeal of his son’s capture.

Of the 251 people Hamas took captive during its attacks on Israel on Oct. 7, 2023, 12 had American citizenship. Mr. Alexander’s 20-year-old son was the last of the 12 still held hostage. Israeli authorities estimate that 59 hostages remain. Dozens, including four American citizens, are presumed to be dead.

“We never lost hope,” Mr. Alexander said on Wednesday, during an interview after his son’s release. “I could not allow myself to think any other way.”

Now, with his son practically right in front of him, Mr. Alexander said that he steeled himself once more.

“I can’t go and cry in front in him,” Mr. Alexander recounted. So he paused for a few minutes to let his wife and oldest son hug in the room down the hall. “I have to stay strong.”