Making first char in each word caps, but not roman numerals

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C#

Does anyone know how I can format the first char of each word in a string to upper case except for roman numerals? The line of code I am using:

fmtedTxt = new System.Globalization.CultureInfo("en").TextInfo.ToTitleCase(txtTitle.Text.ToLower());

This will turn a string "richard III" into "Richard Iii".

Anyone know how to fix this in c#?

Thanks in advance.