Alexa Nikolas was left in tears after Britney Spears apologised for shouting at her on the set of 'Zoey 101' .

The former child star recently opened up about an incident that took place while she was filming the kids TV show more than 15 years ago - claiming Britney yelled at her backstage after Alexa was accused of bullying by the singer's sister Jamie Lynn - her co-star on the show.

Britney has since shared a letter of apology saying sorry to the 30-year-old actress, which left her speechless. In a post on Instagram, Alexa wrote: "@britneyspears I'm sitting here crying with my jaw on the floor. Thank you for seeing me and listening to me. Thank you for apologising. As you know I forgive you. My child self and current self is in awe of the incredible person you are."

Alexa - who denied bullying Jamie Lynn - opened up about the incident with Britney during an episode of the 'Vulnerable with Christy Carlson Romano' podcast, saying she was taken to a room backstage where Britney and Jamie were waiting to confront her.

She said: "It wasn't OK because I was a 12, 13-year-old ... And she was like eight months pregnant, so she was hormonal, too. And I remember she was rubbing her belly while she was yelling, and it was like she was trying to calm herself. And you could just tell, it was very unhinged in a way that felt … like someone was manipulating her."

Alexa added that she was disturbed by the incident and claims it left her feeling unsafe. She added: "I remember looking around and going, 'Wow, nobody cares about what’s happening to me. I don’t feel protected, and I don’t feel safe. I’m scared, and now I have to go back on set and pretend that nothing happened and have to be around those who did it to me'."

Britney went on to add a lengthy note of apology on Twitter, writing: "It broke my heart to see your interview about your experience in the business ... Hollywood is a place of dreams but let's be honest ... on rare occasions do people come out years later and share the dark side!!"

The 'Toxic' singer added: "Just imagine ... me visiting my little sister on her set, last day of shooting, bringing Sprinkles cupcakes ... nine months pregnant, hormones raging like hell and the assistant director lan witnessing Jamie Lynn running to me, placing her hands on my knees while I'm sitting down, her sobbing telling me that she's being bullied on set!!! The assistant director and my mom included in the room were just silent!!! My sister was literally like my daughter growing up ... so I apologise for my ignorance for yelling at you when I obviously had no idea what was really going on!!!"

Britney ended her message writing: "I do write you this message today because I am sorry for ever hurting your feelings!!!"