The British pop star, who found fame in the seven-piece group, announced the arrival of her son Roman with businessman boyfriend Paul Cashmore on her Twitter page on Monday night (20Jun16).
“Proud and excited to announce the arrival of my beautiful baby boy Roman,” Tina wrote, adding some baby bottle and blue heart emojis.
Tina, who turns 40 in September (16), previously admitted her age was a cause for concern as had feared she might have "left it too late" to have children, but told Britain's OK! Magazine, "thankfully that wasn’t the case."
Tina and Paul met in 2012 on the set of a charity music video and they had been discussing marriage, but delayed plans to get hitched after discovering they were expecting a child.
"Before Tina got pregnant we were considering flying to Las Vegas to tie the knot, just the two of us," Paul said, before Tina added, "Things have changed now we’re having a baby – we’d want him or her to be there, so I imagine we’ll do something a bit bigger when the time comes."
Paul also told the magazine he hopes they will be married within a year of the baby's birth.
S Club 7 split in 2003 after five years, but the full seven-piece announced reunion plans in 2014.