Telegram markdown syntax: Bold *and* italic? (September 2018)

That Wiki page is outdated. Telegram accepts standard Markdown text formatting:

• Bold: Double * = **hello world**
• Italic: Double _ = __hello world__
• Monospace: Triple ` = ```hello world```

You can highlight the text and then press the three-dot button in the upper right corner. It will present you with a choice of formatting options. Do it twice and first choose one formatting and then the other. The text will be bold and italic as a result.