The Wepa hitmaker has been invited to belt out Spanish ballad Mas Alla (Beyond) at the star-studded A Journey of Faith show before Pope Francis holds mass at the fabled venue, and Estefan admits she is battling serious nerves ahead of the big gig, which will also feature appearances by Broadway regulars Kelli O'Hara and Norm Lewis and singer James 'D Train' Williams.

"I always pray for the things that everyone prays for - good health for my family, that we become a better world. In this instance, I've also been praying that I don't forget the lyrics," Estefan confessed. "If you don't get nervous before getting up in front of a lot of people, much more so when the Pope is involved, then something is wrong with you. You're not human or something."

The song is the same tune Estefan serenaded Pope John Paul II with back in 1995 and the Cuban-American singer is flattered to have been invited back to perform for the new Pontiff.

In a video message to fans on, she states, "Hi everybody, I am so privileged and honoured and blessed to be singing for my second Pope. I sang for John Paul back in 1995 and now for Pope Francis right here in New York City."

Prior to the Madison Square Garden appearance, the Pope addressed world leaders at the United Nations headquarters, where he called for peace and pushed for action to tackle climate change and global poverty.

He also toured the September 11 Memorial and Museum on Friday, when he met with families whose loved ones were killed in the 2001 terrorist attacks and took part in a multi-religious service with leaders of different faiths.

Addressing the crowd at the event, he said, "This is a place where we shed tears. We weep out of a sense of helplessness in the face of injustice, murder, and the failure to settle conflicts through dialogue. Here we mourn the wrongful and senseless loss of innocent lives because of the inability to find solutions which respect the common good."

He added, "This flowing water (in the memorial's reflection pools) reminds us of yesterday's tears, but also of all the tears still being shed today."