3:35 PM PT -- WWE tells TMZ Sports, "We recently received what appears to be a meritless lawsuit and we will vigorously defend ourselves."

When reached Ric Flair had no comment.

WWE superstar Charlotte Flair is being sued by her ex-husband who claims she defamed him in her new book by falsely claiming he shoots blanks.

It's all in new legal docs filed by Riki Paul Johnson and obtained by TMZ Sports ... in which he goes after Charlotte, her father Ric Flair and the WWE, demanding more than $5 MILLION in damages.

Riki's beef is with the book 'Second Nature' -- which Ric and Charlotte wrote together and released in Sept. 2017.

In his suit, Riki claims the Flairs wrote negatively about his relationship with Charlotte -- and falsely stated that he is sterile and incapable of fathering children.

FYI, Riki and Charlotte -- real name Ashley Fliehr -- were married from 2010 to 2011.

Riki says the allegations in the book have humiliated his family -- including his 3 children -- because they're now the subject of ridicule and shame by people who believe the Flairs.

Riki also claims the book contains "multiple false allegations physical and/or psychological abuse" -- which he believes he can prove based on police reports and dash cam footage.

He also claims the Flairs wrongly claimed he was fired from 2 jobs due to illicit drug use.

In his suit, Riki claims he was intentionally painted as a villain in order to make Charlotte seem like a "victim who overcame personal adversity and domestic abuse."

He also claims WWE was involved in the marketing of the book -- so, they should be held liable as well.