Toni Braxton gained 17lbs for her role in 'Faith Under Fire: The Antoinette Tuff Story'.

The 50-year-old star plays the part of Antoinette Tuff - who persuaded a would-be gunman to not open fire on children in a suburban Atlanta elementary school - in the TV movie, and has revealed she had to transform her appearance in order to appear in the role.

Recalling her own family's reaction to the production, Toni explained: ''They were shocked, they were shocked. It was a heavy role.

''I gained 17lbs for it, I gained five back over the holiday ... what do you call it when I ... I spray-tanned? I spray-tanned my body to make my skin a little darker - that's the aesthetics I did for the role.''

Toni also revealed that she studied Antoinette's behaviour and mannerisms prior to walking onto set.

Appearing on 'Good Morning America', Toni shared: ''I watched everything Antoinette. I watched her interviews, I watched imaging, her interviews with Mr Cooper, Anderson Cooper, the 911 call. She was completely calm.

''I was like, 'How is she so calm?' I think what she was able to do ... she was a negotiator.''

Toni took up acting classes a few years ago after she was diagnosed with systemic lupus erythematosus, a potentially life-threatening autoimmune disease.

Speaking in 2011, she explained: ''I have to be honest, because of my illness I've had to slow down with my performances so I'm doing shows here and there. The most shows I've done are three in a row, one time in a month.

''I haven't toured consecutively in a long time, so I'm like, 'you know what, I'm gonna have to come up with another plan, a new job.' I have to try new things to keep my options open.''