Parker, who was diagnosed with a terminal brain tumour last year, was joined on stage by bandmates Max George, Jay McGuiness, Nathan Sykes and Siva Kaneswaran.
The band – who split in 2014 – shared a group hug on stage when Parker appeared to tear up.
Ed Sheeran, KSI, Liam Payne and Sigrid were among the other stars who also performed yesterday (21 September) in support of the cancer charity.
Following the emotional performance, Parker posted a video of fans outside the London concert hall chanting: “We love Tom!”
Sharing the video on social media, the 33-year-old wrote: “Wow, what a night, thank you all from the bottom of my heart sorry I couldn’t come out and see you all. Covid Covid but thank you all for the support. It means so much xx.”
In October last year, Parker announced that he had been diagnosed with an inoperable stage four brain tumour.
The singer shared his “complete shock” at the news, which came just weeks before his second child with wife Kelsey Hardwick was due to be born.
“There’s no easy way to say this but I’ve sadly been diagnosed with a brain tumour and I’m already undergoing treatment,” Parker wrote.
“We are all absolutely devastated but we are gonna fight this all the way. We don’t want your sadness, we just want love and positivity and together we will raise awareness of this terrible disease and look for all available treatment options.”
The Wanted performed together from 2009 to 2014, during which they released three albums and 12 UK top 20 singles, including the 2011 hit track “Glad You Came”.
The band is due to release a greatest hits album titled Most Wanted on 12 November.
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