The singer, 34, has also thanked fans for their support after rumours began last week.
Hannah's ex-fiancé Adam Thomas told the Sunday People that Hannah kicked him out of their shared flat "out of the blue" and moved Paul in.
And after days of speculation from fans - including circulating snaps of Paul and Hannah kissing on a train - Hannah has admitted she and Paul, 38, have reunited and are living together.
The 'Don't Stop' singer tells the newspaper: "We're really happy together. Everything is great."
Denying Adam's claim she called Paul "the fat one who can't dance", Hannah said: "We're not bothered. No one is going to ruin what we have."
After the upset of her ex-fiancé selling his story to a national newspaper, Hannah says she is grateful for all the support she's had from her fans.
"The reaction from fans has been great," she says. "We've had lots of messages from people saying they glad we're back together. It's so nice."
She also thanked her fans - who have nicknamed the couple Pannah - via Twitter, simply saying she "loves them".
4 words ... I u guys ...— Hannah Spearritt (@hannahspearritt) June 22, 2015
Hannah and Paul were a couple for five years during S Club 7's reign at the top of the charts.
They split in 2006 amid allegations she'd cheated on him with Primeval co-star Andrew Lee Potts, who she later became engaged to.
S Club 7 reunited last year and announced a comeback tour.
It was announced this week that Paul will join X Factor star Diana Vickers and Emmerdale actor Ben Freeman on tour in a production of The Rocky Horror Show.
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