After the climactic sequence in Madison Square Garden that sees all of the adult Godzilla's offspring nuked by the military, the final shot of the 1998 film returns to the Garden to reveal that a single egg remains. It hatches and a baby creature roars.
What It Teased
TriStar had originally foreseen that Godzilla would become a trilogy when they took on the character's rights in 1992 and the ending suggested that we were going to effectively get a Son Of Godzilla sequel. It was designed to be open-ended, just in case the studio wanted to make more.
Despite good box office projections and so much confidence in a sequel that Sony paid Toho $5 million for sequel rights, the planned sequel - which got to the treatment stage and was going to be "remarkably different from the first one" - was dropped because of a lack of enthusiasm from fans, audiences, theater owners, and licensees.