LOS ANGELES (AP) — Marc Maron is locking the gates on his podcast Monday after 16 years and more than 1,600 episodes.

The final episode of “WTF With Marc Maron” is expected to drop in the morning, but its contents, and the identity of his last interview guest (or guests) remains a mystery.

In his penultimate episode on Thursday, the 62-year-old Maron said it was his last from his home studio, but said nothing else about who might show up for his swan song.

Maron’s guests are rarely if ever announced in advance. Fans have been fervently speculating about who they might hear Monday. Could it be an entertainment giant making their first appearance? ( Bob Dylan?Taylor Swift? ) A more personal choice? (An old friend? His parents?) A reprise of a previous major guest? ( Barack Obama? ) Maybe a combination?

On Thursday’s episode, Maron chose to go it solo and talk directly to listeners as he has for several minutes to open every episode.

“We’ve had a relationship for a long time — 16 years,” he said. “That’s the longest relationship I’ve ever had.”

He got emotional several times as he spoke.

“I’m grateful to have been part of your lives,” he said. “We’ve been through a lot of stuff together. A lot of breakups. Death. Cats. The world.”

The final episode will be No. 1,686 of the pioneering and influential long-form interview podcast that had humble beginnings in 2009 as a place where he worked out his issues with other stand-up comedians in the garage of his Los Angeles home that he dubbed “The Cat Ranch.”

For most of its years the show has opened with a fan-composed rock ‘n’ roll theme song that opens with an audio sample of Maron in his small role in the film “Almost Famous” shouting, “Lock the gates!” The song is named for one of Maron’s common phrases, “Are We Doing This?” Another such phrase, “Are we good?” was often his last question to guests and is the title of a new documentary on him.

Eventually, “WTF” became a media institution where authors, artists, musicians, Hollywood stars and political leaders would give him their backstory.

Maron announced in June that he and longtime producing partner Brendan McDonald had decided to end the show. He said there was no particular reason, other than that he was tired and utterly satisfied with the work they had done.