The 14-year-old from Telford was crowned the under-55kg world champion last month after a third round stoppage in a dominant performance.
Underwood, who trains at JBS Martial Arts Academy, has added to his haul of gongs that also include the English, British and European belts.
After starting training at six-years-old, the teenager is now working towards becoming a professional kickboxer in the future.
His step-mother and coach, Joanne, said: "When he's training for a fight he's training six days a week and has to cut weight safely through diet and exercise.
"He's very determined, it's what he wants to do and that's why he's so successful in it.
"It was absolutely amazing when he won his world title, absolutely overwhelming. It was all worthwhile!
"All the work paid off for him, the weight cut, the hard training, it all paid off. I'm over the moon for him and so proud.
"It's really difficult to do what he's done because at that age kids are growing and want to eat what they want.
"But Taylor wants to be a professional fighter and to go down that route at 14 by cutting weight and winning titles, is amazing.
"I think he'll do it and become a professional kickboxer. I can't match him with anyone in the UK right now, he's unbeaten with 18 wins and one draw.
"He puts everything into it and always gives 110 per cent. There's never any time I have to motivate him and it helps because it's what he really wants to do.
"He knows he needs to work now to achieve his dream. He loves it."
Underwood is fighting again at the end of this month for another English title at an event in York.