The Latino pop star and the R&B singer, who announced earlier this week (12Oct15) he's set to become a first-time dad, will perform at Clinton's upcoming 68th birthday party at New York City's Hilton Midtown Manhattan on 25 October (15), the day before her actual birthday.

An invitation obtained by People magazine, suggests the former Secretary of State "might even dance" at the event, which will also serve as a campaign fundraiser.

"Some women don’t like to discuss their ages, but I think that on your birthday, you should live it up!," Clinton writes. "This year, I'm excited to celebrate the fact that I’m running to be the youngest woman ever to be President of the United States."

Lovato and Legend join the growing list of celebrities who are showing their support for Clinton, with stars such as Tom Hanks and Rita Wilson, Jessica Alba, Christina Aguilera, Sharon Stone and Lady Gaga also campaigning for the Democratic candidate.