David Letterman, an institution of late night television for three decades, announced during his show Thursday that he is retiring when his contract expires in 2015.

Letterman announced the news while taping tonight’s Late Show. CBS has not officially announced it, but TV Line reports that bassist Mike Mills broke the news on Twitter. Mills, the former bassist for REM, is performing during the show with Joseph Arthur.

Back in October, Letterman signed a deal with CBS to continue hosting Late Show through 2015.

Letterman is the longest-tenured late night host in TV history. He started hosting his own show, NBC’s Late Night in 1982 and won five Emmys during the 11-year run. He moved to CBS after Jay Leno replaced Johnny Carson on The Tonight Show and celebrated 20 years on CBS last year.

Letterman will leave behind a noticeably younger late night environment, as Leno just left The Tonight Show. Jimmy Fallon took over in February.