This is going to sound really dumb but

From Wikipedia.

HammerFall began when guitarist Oscar Dronjak quit Ceremonial Oath and invited Jesper Strömblad (from In Flames, also originally a member of Ceremonial Oath) to join him on a new musical project which he had been idealising for some time. Dronjak had already composed the song "Steel Meets Steel", which was later included on HammerFall's debut album. They were later joined by guitarist Niklas Sundin, bassist Johann Larsson and vocalist Mikael Stanne (from Dark Tranquillity). When Niklas Sundin and Johann Larsson quit HammerFall the following year, Glenn Ljungström (ex-In Flames) and Fredrik Larsson (the bassist of the former Swedish death metal band Dispatched) replaced them.
Both Dronjak and Strömblad took part in other bands at the time: the relatively unsuccessful Crystal Age from Dronjak and the band which to a great extent influenced Swedish melodic death metal, In Flames, from Strömblad. Thus, HammerFall was relegated to being a side project of them both for several years. Their concerts were limited mostly to a local music contest named Rockslaget. The band had few songs of their own and played mostly covers from bands such as Pretty Maids, Judas Priest and Alice Cooper.
In 1996, HammerFall reached the semi-finals of Rockslaget. However, it was soon found that vocalist Mikael Stanne was not going to be able to perform with the band on the semi-finals. Hence, they began the search for a replacement. Through mutual friends, they got in contact with Joacim Cans, who agreed to play with them for the night. The concert was a success, despite the fact that the judges didn't qualify HammerFall for the finals. By the end of that day, Joacim had already been made an official member of the band.
 
i have always wondered if this expression comes from because the 2 words exist in French, but the sentence would be grammaticaly wrong in French, and i found this
but i always thought that Caesar said "tu quoque, fili" or something close.

Nah, I said "et tu, Brute?" :D

They omitted it in the HBO's Rome... no wonder their ratings werent that high :S

And - how interesting (same source): "The phrase is often misquoted as "Et tu, Brutus?" Brute is the Latin vocative form of Brutus, used when directly addressing the individual in question. The nominative form, Brutus, would be used in a sentence such as "Brutus killed Caesar," where Brutus is the grammatical subject of a verb."
 
^ You are correct.

The vocative case is used for direct address. It is rarely the first word in a sentence and is usually set off by commas. The vocative case in Latin is the same as the nominative in all declensions, except for second declension singular nouns ending in -us or -ius. Nouns of the second declension singular ending in -us have -e as the vocative ending, as amice, O friend
But filius and proper nouns ending in -ius, have the vocative ending in -i: fili (my) son: Iuli, Julius
 
That's very useful information. I once had "Skeleton of Society" as my user title at some other forum, be sure to write that down!