The 'Without Me' hitmaker appeared on 'The Ellen Degeneres Show' and the host pulled a Halloween prank on Halsey by getting a lookalike of the 'American Horror Story' actor to jump out on her as she was discussing a picture of her and Evan dressed as Sonny and Cher.
Halsey then laughed: ''You distracted me with the boyfriend question.''
And Ellen quipped: ''That's what you called the one-two-punch.''
The pop star then admitted: ''Yeah, I don't know what's scarier though, having to talk about my boyfriend on TV or having that happen. That was a double whammy.''
The couple made their red carpet debut at the 100th episode of 'American Horror Story' celebration at Hollywood Forever in California at the weekend.
Their romance comes after Halsey's ex-boyfriend Yungblud revealed their split was ''mutual'' and they are still ''good mates''.
The 22-year-old musician - whose real name is Dominic Harrison - and the 'Nightmare' hitmaker broke up earlier this year after almost one year of dating, and he said the decision to part ways came as they were both ''too busy'' and had ''too much going on'' to commit to a romance.
He said: ''Me and my ex-girlfriend are good mates now. That ended mutually. We had too much going on. We were too busy.
''We were going on our own missions. She's doing her thing, I'm doing my thing and in terms of it, I'm feeling love from everywhere.
''I get so much love from my fan base right now.''
Halsey recently took to Twitter to post a now-deleted message, in which she explained that she and her former beau are still friends despite their split.
The tweet read: ''Sometimes. People just break up. It doesn't mean someone cheated or something bad happened or someone f***ed up.
''Sometimes. It just happens. Because life is constantly changing. And adults stay friends and move on.''
She later added: ''Now u know what u know (sic)''
The 24-year-old star - who collaborated with Yungblud on their song '11 Minutes' in February this year - has been romantically linked to Evan, who split from his former fiancee Emma Roberts in March, for a number of weeks, after they were spotted together in Sherman Oaks, California.
An insider said: ''Halsey and Evan were at Sweet Butter Cafe in Sherman Oaks. They definitely looked like a couple.
''They were eating together and Halsey was laughing throughout their lunch. When they walked out of the restaurant they were hugging each other.''