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It's Wonderful Christmastime! Reese Witherspoon and Scarlett Johansson join Paul McCartney for all-star cappella

Sharnaz Shahid

With Christmas just around the corner, the stars are well and truly in the festive spirit. Reese Witherspoon and Scarlett Johansson joined Paul McCartney for an a cappella rendition of his hit song, Wonderful Christmastime, on The Tonight Show Starring Jimmy Fallon.

The two actresses were joined by their Sing! co-stars Matthew McConaughey, Seth MacFarlane and Tori Kelly, as well as the band The Roots in the special segment, which aired this week. Over the past few weeks the actors and musicians have been busy promoting their latest venture.

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In the upcoming animation, which is based on an animal singing competition, Reese lends her voice to Rosita, a shy mother-of-25 piglets, while Matthew takes on the role of Buster Moon, a koala who is trying to prevent his theatre from shuttering down. The Universal Studios comedy also stars Jennifer Saunders and Seth MacFarlane and is expected to hits US cinemas on December 21 and in the UK on January 27.

During the promotional rounds, Reese, 40, opened up about the pressures of parenting, and revealed that sometimes tough love is the best way to raise her three children. "We have rules around the house," she told Entertainment Tonight. "I always say if you aren't yelling at your kids you're not spending enough time with them. [I'm] just telling everyone to clean up all the time."

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The stars of Sing! came together for a special Christmas skit

The Hollywood beauty is mother to 17-year-old Ava, 13-year-old Deacon and four-year-old Tennessee. "People know not to call me before 8:15, because 8:15 is when everybody needs to either be on the bus or at school and then my whole life starts at 8:15," she added.

Reese, most famous for her role in Legally Blonde, has also been busy producing and starring as Madeline Mackenzie in Big Little Lies, which is based on the bestselling novel of the same name by Liane Moriarty. The story follows three mothers who have children in the same class at school but their 'perfect lives begin to unravel.' The tension between the parents slowly grows until a murder is committed.