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The official UK website states that Brazilian citizens do not need a visa to visit the UK for up to 6 months. It goes on to mention documents that may be needed at the UK border:
You must provide a valid passport or travel document. Your passport should be valid for the whole of your stay in the UK.
You may also be asked to prove that:
- you’re visiting for tourism
- you’re able to support yourself and your dependents during your trip (or have funding from someone else to support you)
- you’ve arranged accommodation for your stay
- you’re able to pay for your return or onward journey (or have funding from someone else)
- you’ll leave the UK at the end of your visit
So yes, as you’re hosting his stay you should provide an invitation (which does not need to be notarised), and your guest should bring documents to prove he meets the other eligibility criteria eg bank statements, employment contract etc, if asked.