Are we right in assuming that the beam is supported at it's end; this is such an odd cockup, that everything may not be as straightforward as it seems. I suspect Hondas suggestion of a window box seat may the best option.
An angle grinder with a cutting disc of course, would have that up in no time. Not that the OP should though, the beam will be weaker and twistier for it as loads of folk have stated.
Look around for the very thin cutting discs - less then 2mm thick they work really well. You can get them in a tin (!!) 10 for £5 at cheapo tool stands in markets.
Frank
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