Katharine McPhee performs at stepdaughter's wedding

Katharine McPhee performed at her stepdaughter's wedding on New Year's Eve (31.12.19).

The 35-year-old actress took to the stage at Erin Foster's wedding, where she serenaded the guests - who included her husband David Foster - during the reception.

Another of the big-name wedding guests, Kate Hudson, also performed at the bash, whilst the bride even led a group karaoke rendition of TLC's 'No Scrubs' to mark the special occasion.

The wedding was also attended by Hollywood star Jonah Hill, fashion designer Rachel Zoe and make-up artist Aliana Lopez, as well as Erin's mother Rebecca Dyer and her older sister.

Katharine and David tied the knot themselves earlier in 2019, and the actress previously revealed she decided to take David's surname because she loves the "traditional" nature of taking a partner's last name.

Asked why she decided to take his surname, Katharine said: "I'm a romantic. I've always liked the idea that it's still a traditional thing that exists in our society. I like the idea.

"I think it's romantic and it's a great last name ... We've been away since we've been married, so not [yet], but I love it. I just love the ring of it, so I'm enjoying it."

Meanwhile, David's other daughter, Sara, previously sung Katharine's praises.

Sara said: "She's great. She's a great addition.

"You know I've learned to not rule anything out [about kids]. I think anything is possible at this point. Who knows? ... She's wonderful.

"The other day she was like, 'I got you a facial,' and like that's so cool. My dad loves love and my dad loves commitment. My dad's always been married. He's never been single really.

"He's a real commitment, marriage kind of guy and I'm happy for him."