Proof of Citizenship - Partner from NI

Hi! I'm applying for an unmarried partner visa from the US. My partner is both a British and Irish citizen by birth (from Northern Ireland) but only has an Irish passport. I was wondering if it would likely be necessary to submit further proof that my partner is a British citizen in my supporting documents? I've listed the address we plan to live at in Northern Ireland and mentioned that he owns this house and the Northern Irish county of his birth is listed on his passport, if this changes anything. Thanks in advance for the help!