Well, did it actually remove Ubuntu from your hard drive, or just the entry in the grub.conf? If it didn't remove your entire installation: You can probably mount the Ubuntu partition(s) in Fedora and copy the lines directly from one grub.conf to the other. For instance, if the partition containing the grub.conf for Ubuntu is /dev/sda3, you could do:
mount /dev/sda3 /mnt
Then, find the grub.conf in that filesystem and copy the lines to boot Ubuntu into the Fedora grub.conf.
On newer versions of grub, grub.conf is also called menu.lst