Geri Halliwell says she was holding back the tears when she watched the workshops of the new musical.
Mel C added that the rehearsals gave the girls "goosebumps" and it was a "lovely thing"
The girls said the musical supports Girl Power's longevity. "Who would have thought the message is still standing 16 years later".
More top news
Uplifting messages greeted commuters on the London Underground a day after the terror attack in Westminster.
Faith leaders from across London say religious communities will "stand together" in the wake of the Westminster terror attack.
Pc Keith Palmer was among the three people killed yesterday in the Westminster terror attack.