VIDEO: Matt Bomer Talks HBO's THE NORMAL HEART on Fallon

Matt Bomer stopped by last night's TONIGHT SHOW STARRING JIMMY FALLON and talked about losing, and regaining, a lot of weight for his role in the upcoming HBO film The Normal Heart. "I fasted for 21 days and then went on an extremely regimented diet consisting of about 300 calories a day," Bomer explained, to which Fallon quipped, "That's two bites of my lunch!"

Watch the appearance below!

The HBO original film, The Normal Heart, premieres Sunday, May 25th at 9PM/8C, only on HBO. Today, the cable network shared a behind-the-scenes look from the set of the highly anticipated drama. Check it out below!

Directed by Ryan Murphy and written by Larry Kramer, adapting his groundbreaking Tony Award-winning play of the same name, THE NORMAL HEART, tells the story of the onset of the HIV-AIDS Crisis in New York City in the early 1980s, taking an unflinching look at the nation's sexual politics as gay activists and their allies in the medical community fight to expose the truth about the burgeoning epidemic to a city and nation in denial.

The film stars Academy Award nominee Mark Ruffalo ("The Kids Are All Right"), Matt Bomer ("White Collar"), Taylor Kitsch ("Lone Survivor"), Emmy(R) winner Jim Parsons ("The Big Bang Theory") and Academy Award winner Julia Roberts as well as Alfred Molina ("An Education"), Tony Award winner Joe Mantello ("Law & Order"), Jonathan Groff(HBO's "Looking"), Denis O'Hare (HBO's "True Blood"), Stephen Spinella ("Milk"), Corey Stoll ("House of Cards"),Finn Wittrock ("Unbroken"), and BD Wong (HBO's "Oz").

An HBO Films presentation of a Plan B and Blumhouse production in association with Ryan Murphy Productions, THE NORMAL HEART is executive produced by Ryan Murphy, Dante Di Loreto ("Glee"), Jason Blum (the "Paranormal Activity" series), Brad Pitt ("Moneyball"), Dede Gardner ("12 Years a Slave"). Mark Ruffalo co-executive produces; Scott Ferguson (HBO's "Temple Grandin") produces.