Database Size Increase After Index Rebuild

Hi

I recently perfomed an Index Rebuild using a Maintenance Plan on a large table in my database because it was 91% fragmented. After the Index Rebuild the database file increased in size from 18605 MB to 32364 MB.

The Index Rebuild was set to 'Reorganise pages with the default amount of free space'.

Is there anyway to stop my database increasing in size as a result of my Index maintenance?