A letter from the mother of an autistic child thanking a fellow passenger on a flight for his patience and compassion has gone viral, even reaching its addressee, 'Daddy in Seat 16C'.

Shanell Mouland was on a flight back from a trip to Disney World in Orlando, Florida, and was on her way home to Brunswick, Canada with her three-year-old daughter Kate.

In a heartfelt post on her blog Go Team Kate, entitled 'Dear Daddy in Seat 16C', Ms Mouland, 36, thanked the mystery passenger who was sat next to Kate for the duration of the flight.

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Ms Mouland said she had to sit her daughter in the middle passenger seat because Kate was becoming fixated with the window shutter, leaving her anxious her daughter's mood or behaviour could upset the person who would sit next to her.

But Ms Mouland said a business man then sat in the spare seat and went out of his way to engage with Kate and accommodate her needs for the whole journey.

In the post, Ms Mouland writes: "I don't know your name, but Kate called you "daddy" for the entire flight last week and you kindly never corrected her.

"In fact, you didn't even flinch as you could probably tell that she was not confusing you with her own 'daddy,' but instead making a judgment regarding your level of 'safety' for her. If she calls you 'daddy' then you better believe she thinks you are alright."

The 'Daddy' Ms Mouland addressed the letter has since been identified as Eric Kunkel, a married father from New Jersey. After being alerted to the post by his relatives, he said: "I travel a lot for work, and Kate was, by far, the most well-behaved kid I've sat next to. Shanell is also an incredible parent — she didn't apologize for Kate and she shouldn't have — but she was very attentive to her."

The letter continued: "I watched the entire Temple basketball team board the plane, and wondered if one of these giants might sit by Kate. They all moved toward the back.

"She would have liked that, she would have made some observations that I would have had to deal with, but she would have liked those players. I watched many Grandmotherly women board and hoped for one to take the seat but they walked on by.

"You could have shifted uncomfortably in your seat. You could have ignored her. You could have given me that 'smile' that I despise because it means; 'manage your child please'. You did none of that. You engaged Kate in conversation and you asked her questions about her turtles.”

Mr Kunkel said he contacted Ms Mouland via Facebook and they have now become good friends.