Fallout Shelter was the first mobile game that Fallout 4 and Skyrim developer Bethesda Game Studios ever created and it won't be the last. Director Todd Howard revealed last year that the studio is making more mobile games. These have not been announced just yet, but in a new interview with GameSpot, Howard recalled the huge success of Shelter and teased the studio's next mobile title.

"We loved making it so we were ecstatic when it was so successful," Howard said about the free-to-play Shelter. The game was released for iOS and Android devices in 2015; as of June 2016, it had more than 50 million registered players. Bethesda doesn't provide specifics, but reports have said the game has made millions of dollars, with revenue coming from microtransactions.

"It kind of blew us away," Howard said about the reaction to Shelter.

He added that the key to long-term success in the mobile market (and elsewhere) is to continually release new updates to keep players engaged. Bethesda has definitely done that, as Shelter has been supported with lots of seasonal updates and other patches.

Shelter still has a "pretty active player base," Howard said.

Looking ahead, Howard teased Bethesda's second mobile game, saying it's something that the studio has had in mind for a long time.

"We do have another mobile project game that we thought about for a while," he said. "Based on the Shelter experience, we're kind of rolling on something new."

It remains to be seen which studio is working on the new mobile game. In December 2015, Bethesda Game Studios opened an office in Montreal with an aim to "expand its development capabilities in console, PC, and mobile gaming."

In other news about Shelter, the game recently launched for Xbox One and Windows 10 as a Universal Windows Platform app. The game may not come to PlayStation 4.