The pair, who starred in the 2009 rom-com "The Proposal" together along with White, reunited on Instagram to sing a rendition of the song in celebration of her big day.
The video starts with Bullock and Reynolds switching back and forth singing the beginning of "Happy Birthday," but takes a hilarious turn when they start competing for who loves the 98-year-old the most.
"From Sandy, who loves you more than Ryan," Bullock says. But Reynolds tries to one-up her saying, "From Ryan, who loves you so much more than Sandy."
"What does Sandy do for you every year?" the "Deadpool" actor continues. "I mean, does she like show up and hand-deliver flowers for you wearing nothing but black socks and a dozen gold bracelets, just like you requested? Doubt it."
"I love you! Happy birthday! Mwah!" Bullock concludes. For his part, Reynolds fake cries to the camera.
The video ends with the "Golden Girls" theme song playing along with a graphic that says: "Happy 98th Birthday Betty!"
Reynold's, who plays White's grandson in "The Proposal" has made it a tradition to wish his former co-star a Happy Birthday each year. In 2018, he paid tribute to White with a Deadpool-themed birthday message. Last year, he shared a photo with White saying he doesn't usually wish "ex-girlfriends Happy Birthday. But Betty’s special."
STUDIO CITY, CA - JANUARY 16: Actress Betty White poses at the celebration of her 93rd birthday on the set of 'Hot in Cleveland' held at CBS Studios - Radford on January 16, 2015 in Studio City, California. (Photo by Mark Davis/Getty Images for TV Land)
BETTY WHITE -- Pictured: Actress Betty White c. 1954 -- (Photo by: NBC/NBCU Photo Bank via Getty Images)
CULVER CITY, CA - MAY 09: (EXCLUSIVE COVERAGE) Betty White attends Betty White fashion shoot for The Lifeline Program at Smashbox Bigbox on May 9, 2012 in Culver City, California. (Photo by Brian To/Getty Images for The Lifeline Program)
OFF THEIR ROCKERS -- 'Betty's House' Episode 201 -- Pictured: Betty White -- (Photo by: Justin Lubin/NBC/NBCU Photo Bank via Getty Images)
LOS ANGELES - DECEMBER 2: Actress Betty White sits down with the hosts of THE TALK, Monday, Dec. 2, 2013. Betty White shown. (Photo by Sonja Flemming/CBS via Getty Images)
TODAY -- Pictured: (l-r) Hoda Kotb, Kathie Lee Gifford and Betty White appear on NBC News' 'Today' show -- (Photo by: Peter Kramer/NBC/NBC NewsWire via Getty Images)
STUDIO CITY, CA - AUGUST 04: Actress Betty White attends the 'Hooray for HollyWOOF!' 35th Anniversary Gala Fundraiser for Dogs for the Deaf at The Sportsman's Lodge on August 4, 2012 in Studio City, California. (Photo by David Livingston/Getty Images)
LOS ANGELES, CA - JANUARY 07: (EDITORS NOTE: This image was processed using digital filters.) Actresses Betty White and Ellen DeGeneres attend The 41st Annual People's Choice Awards at Nokia Theatre LA Live on January 7, 2015 in Los Angeles, California. (Photo by Chris Polk/Getty Images for The People's Choice Awards)
LOS ANGELES - FEBRUARY 19: Actress Betty White presents at the 57th Annual Writers Guild Awards at the Hollywood Palladium on February 19, 2005 in Los Angeles, California. (Photo by Kevin Winter/Getty Images)
A headshot portrait of American actor Betty White wearing a veiled hat, circa 1955. (Photo by Hulton Archive/Getty Images)
LOS ANGELES - MARCH 2: Actress Betty White arrives at the premiere of her movie 'Bringing Down The House' on March 2, 2003 in Los Angeles, California. (Photo by Dan Steinberg/Getty Images)
LOS ANGELES - DECEMBER 17: Betty White with Craig Ferguson on THE LATE LATE SHOW WITH CRAIG FERGUSON, scheduled to air Wednesday, Dec. 17, 2014 on the CBS Television Network. (Photo by Sonja Flemming/CBS via Getty Images)
LOS ANGELES, CA - JUNE 14: Actress Betty White attends the Greater Los Angeles Zoo Association's (GLAZA) 44th Annual Beastly Ball at Los Angeles Zoo on June 14, 2014 in Los Angeles, California. (Photo by Angela Weiss/Getty Images)
US President Barack Obama talks with acclaimed actress Betty White in the Oval Office of the White House June 11, 2012 in Washington, DC.
THE PROPOSAL (2009) SANDRA BULLOCK, BETTY WHITE ANNE FLETCHER (DIR) 005