Chelsea Clinton announced Thursday that she and her husband are expecting their first child this year — as her parents, the former and possibly future presidents, prepared to become grandparents.

In a surprise announcement, Clinton, 34, said she and husband, Marc Mezvinsky, are “very excited” and “lucky” to welcome a child into their family.

“I just hope that I will be as good a mom to my child and hopefully children as my mom was to me,” said Clinton, as her mother, former secretary of state Hillary Rodham Clinton, looked on proudly. A Clinton spokesman said the baby is due this fall.

The pregnancy coincides with Hillary Clinton’s deliberations about a second presidential campaign in 2016, when she would be the overwhelming favorite for the Democratic nomination.

Thursday’s joyous announcement came at the conclusion of a forum, moderated by actress and activist America Ferrera at the Lower Eastside Girls Club, promoting young women’s empowerment.

At a Clinton Foundation event, Chelsea Clinton announced she’s expecting her first child. She was at the event with her mother, former secretary of state Hillary Clinton. (Pamela Kirkland/The Washington Post)

“I certainly feel all the better — whether it’s a boy or girl — that she or he will grow up in a world full of so many strong, young female leaders, so thank you for inspiring future generations, including the one that we’ll be lucky enough to welcome into our family later this year,” Chelsea Clinton said.

As Clinton spoke, her mother beamed from the stage. She said she was “really excited” to be expecting her first grandchild and later tweeted: “My most exciting title yet: Grandmother-To-Be!” Former president Bill Clinton tweeted: “Excited to add a new line to my Twitter bio . . . grandfather-to-be!”

For some time now, the Clintons have been looking forward to become grandparents. Last year, Chelsea Clinton said in an interview with Glamour Magazine that 2014 would be “the year of the baby,” which stirred much speculation. But she offered no public clues in recent weeks that she was pregnant.

Last month, when late-night comedian Jimmy Kimmel interviewed the three Clintons together at a Clinton Global Initiative University gathering in Arizona, Hillary Clinton said: “I wouldn’t mind one of those grandchildren I’ve been hearing so much about.”

Chelsea interjected playfully that her mother was “shameless” in wanting a grandchild and was “unapologetic in public and in private.”

Chelsea’s announcement Thursday came as a surprise to some senior Clinton staffers working at the event, but there was one sign she had decided that she wanted to break the news there. Midway through the event, Mezvinsky quietly walked into the room through a back door to watch Chelsea share their secret.

Several longtime and loyal Hillary Clinton aides were present, including Huma Abedin, who is so close to the family she is sometimes described as Chelsea’s big sister. Offstage, Hillary, Chelsea and Abedin hugged each other and laughed as they celebrated the news.

Also in attendance were veteran Clinton adviser Capricia Marshall and Vogue editor Anna Wintour. Hillary and Chelsea Clinton hugged Wintour and chatted for several minutes with her, Abedin and journalist Jonathan Van Meter.

Moments later, in an interview, Wintour said it was “so exciting” that a Clinton baby is on the way.

“I’m so thrilled,” Wintour said. “I know that Secretary Clinton has wanted a grandchild for a long time.”

Chelsea Clinton has been in the public eye since arriving at the White House as a teenager, and went on to receive several degrees and settle in New York, where she worked for several years in finance.

In July 2010, she married Mezvinsky, a hedge fund manager and the son of two former members of Congress. They live with their dog, Soren, in a sprawling apartment overlooking Madison Square Park. Mezvinsky’s mother, Marjorie Margolies, is running for Congress this year in a suburban Philadelphia district. She tweeted Thursday that she is “one very proud grandmother-to-be.”

Chelsea Clinton has taken on a prominent role at the family’s philanthropic foundation, serving as vice chair, speaking about its humanitarian work in many public forums and directing an array of global programs, including on health care and women’s issues.

At Thursday’s event, Chelsea and Hillary Clinton answered questions and offered advice to scores of teenage girls, many of whom joined via Skype from schools across the country. This was the first in a series of conversations Hillary and Chelsea Clinton are convening around the world through their family foundation’s “No Ceilings” women’s and girls’ initiative.

At one point, Hillary Clinton urged the young women to “speak out against meanness, speak out against pettiness, speak out against discrimination and prejudice and try to get other people to agree with you that we just don’t have time for that kind of nasty behavior between and among people.”

At an intimate party later to celebrate the premiere of “Of Many,” a film that Chelsea helped produce, the mother-to-be basked in congratulations. Hillary Clinton accompanied her daughter to the party, sipping white wine, mingling with guests and talking at length with her son-in-law.