Shares of GameStop (GME) and other meme stocks popped on Thursday after Roaring Kitty, the online alias of meme stock ringleader Keith Gill, posted to X for the first time since September.

Shares of GameStop jumped as much as 14% Thursday afternoon while AMC Entertainment (AMC), another favorite among meme stock traders, surged as much as 13%. Shares of online pet retailer Chewy (CHWY), also a meme stock favorite, were unaffected.

Gill, at 1:45 p.m. ET on Thursday, posted a photo of a fake TIME Magazine cover featuring just a desktop computer monitor and keyboard. As of 3:45 p.m., the post had been viewed 3.1 million times.  

Gill has repeatedly sparked meme stock rallies by posting cryptic messages and images to X, where he has 1.6 million followers. The last frenzy came in early September when he posted a photo that was taken by some as a sign that he had sold some of his sizable position in Chewy. That post sent Chewy stock plummeting and GameStop soaring. 

After becoming one of the faces of the 2021 meme stock craze, Gill took a long hiatus from public life. He returned to X with a torrent of posts in May and has since sporadically posted, each time setting off a flurry of speculation.

GameStop and AMC pared their gains later in Thursday's session. They were up 6% and 5%, respectively, at 3:45 p.m. ET.