Katharine McPhee dances in underwear backstage at Waitress and jokes David Foster 'won't like this' By Sameer Suri For Dailymail.com Published: 17:04 GMT, 2 March 2019 | Updated: 17:04 GMT, 2 March 2019 Viewcomments She is in previews for the London run of the Broadway musical Waitress. But Katharine McPhee still managed to scrape together a bit of downtime on Saturday, dancing in her underwear in her dressing room. The 34-year-old posted her backstage routine to her Insta Stories and teased her 69-year-old music mogul fiance David Foster in the caption. 'Feeling spicy': Amid previews for the London run of Waitress, Katharine McPhee managed to scrape together a bit of downtime Saturday, dancing in her underwear in her dressing room She vamped: '@davidfoster won't like this,' adding that she was 'Feeling spicy today!' and was heading into a '2 show day let's do this'. Katharine, whose future stepdaughters Erin and Sara Foster are older than she is, stepped into the Broadway production of Waitress for a limited run last year. Waitress opened on Broadway in 2016 with Jessie Mueller in the lead role of Jenna Hunterson - the part Katharine played from April to June last year. Waitress was adapted from Adrienne Shelley's 2007 movie starring Keri Russell, Nathan Fillion, Cheryl Hines, Jeremy Sisto and the Andy Griffith. Frisky: The 34-year-old posted her backstage routine to her Insta Stories and teased her 69-year-old music mogul fiance David Foster in the caption Katharine's brief run in Waitress, which features a Tony-nominated score by Sara Bareilles, marked the Smash star's debut on the Great White Way. Jack McBrayer, most famous for his role as Kenneth on 30 Rock, is in the West End production amid a cast of New York and London stage talent. Previews for this run kicked off on February 8 ahead of the show's official opening at the Adelphi Theatre this coming Thursday, Playbill reports. Incoming: Previews for this run kicked off on February 8 ahead of the show's official opening at the Adelphi Theatre this coming Thursday, Playbill reports The original Broadway run had the misfortune to compete at the same Tony Awards as Hamilton, which beat it for best score and best musical that year. Nevertheless, that New York production was a box office success and is running to this day, with U.S. national tour still in progress as well. Katharine, who was pap-snapped kissing her married Smash director Michael Morris while she was still with her husband Nick Cokas, subsequently got divorced and eventually wound up with David, who is three divorces ahead of her. She confirmed their engagement during a European vacation in July where Foster proposed on top of a mountain in Anacapri, Italy. Love at last: She confirmed their engagement during a European vacation in July where Foster proposed on top of a mountain in Anacapri, Italy; seen in September Read more: Share or comment on this article: All rights reserved for this news site dailymail and under his responsibility