The Saturdays star was in complete disbelief when she found out her real bra size after being measured on Loose Women.
The panelist discovered her cup size on the ITV daytime show this week, with her fellow hosts Judi Love, Nadia Sawalha and Jane Moore.
On Friday’s episode, the former Strictly Come Dancing contestant explained she doesn’t normally wear bras and they were ‘always the first thing’ she took off when she returned home.
Admitting when she was younger she wanted a larger cleavage, the 33-year-old said she stopped longing for a more ample chest when she was pregnant.
‘All I ever wanted was bigger boobs and then when I was pregnant they were massive and I hated them’ she explained.
The S Club juniors singer predicted she was a 32C before a professional from lingerie brand Bravissimo revealed she was actually a 30E.
Frankie could not hide her shock and held her head in her hands in surprise when she was informed of her real size.

She joked: ‘Oh my god, I’m Jordan,’ in reference to Katie Price’s former name as a glamour model.
Judi and Nadia were both in hysterics, with the comedian quipping: ‘Get the tent out.’
Frankie continued: ‘I thought I had itty bitty t*****s.’

On Thursday’s instalment of the long-running series, Strictly 2022 contestant Kaye Adams was overjoyed to discover that she’d gone up over two bra sizes.
The 59-year-old was being measured for outfits on the dancing competition series when she learned she was a 32DD and not the 36B size she’d thought.
Telling her Loose Women co-star’s about the revelation, Kaye realised Jane and Nadia didn’t believe her, exclaiming: ‘Excuse me!’
‘I’ve even got the producer in my ear telling me I’m not a double D,’ Kaye admitted in the hilarious episode.
Loose Women airs weekdays at 12.30pm on ITV