Stevie Wonder has announced he will undergo a kidney transplant later this year.
The American chart-topper told fans of his condition as he wrapped up his set at British Summer Time in Hyde Park.
He told the crowd he had a donor and that he would perform a few more shows before he takes a break ahead of the procedure planned for September.
Wonder said: "I'm all good, I'm all good, all good, I have a donor and it's all good.
"I want you to know, I came here to give you my love and thank you for your love.
"I love you and God bless you."
The news was greeted by cheers of support from fans, who gave him a raucous applause as he was led off stage.
Last week it was reported that Wonder was battling a serious but manageable health issue. The
singer was “doing better now than he was a couple of months ago,” a source told the Detroit Free Press, adding he had been traveling with a medical team.
Wonder's appearance saw him headline the Hyde Park event in the second of five major concerts at the London park.
He had the crowd cheering as he treated them to classics like For Once in My Life, and Master Blaster.
Wonder stopped repeatedly between tracks to thank fans for their support over the years.
He did seem less ebullient than in the past and made his health announcement in a somber tone with a severe look on his face. But he was smiling as he left the stage with the band playing the memorable conclusion of "Superstition" one final time.
His show, called The Song Party, was supported by Lionel Richie - who warmed up the crowd - on the Great Oak Stage on Saturday.
In December 2017, Wonder performed a cover of Easy at Richie's Kennedy Centre Honours ceremony, which left Richie visibly emotional.
He later said: "I got into the business because I wanted to be like Stevie Wonder, so for all of a sudden for Stevie to be singing my song, it was surreal."
His set also featured a tribute to
musicians who have died, including songs by Michael Jackson, Amy Winehouse, Prince and Aretha Franklin.
Like Celine Dion the previous night, Wonder, who has amassed worldwide sales of more than 100 million units, sang John Lennon's Imagine.
The rest of the concert series will see Barbra Streisand perform on Sunday, Florence + The Machine on July 13, and Robbie Williams on July 14.