Raising under market rent

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We have a tenant who's been paying under market rent. 4-5 years ago when we first rented out the unit, the neighborhood was still pretty rough and we were happy that we got someone who was mature, responsible and could pay rent on time. We've never raised the rent on them (rookie mistake) because they would help would help out with shoveling, putting out the garbage. Now the market has totally shifted: high demand, a lot higher rents. Suddenly we're about (gulp) 30% under market rate rent. 

The renter loves the property, takes good care of it and has never had an issue with payment. We do plan on raising the rent at least 10%, but we suspect that even that will be hardship on them. 

What would you do?