Watch Justin Long Do Kate Bosworth's Makeup for Oscars Party: 'You're Putting Lip Liner on My Eyebrow'

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Justin Long has a new way of expressing his love for girlfriend Kate Bosworth.

Ahead of their appearance at Vanity Fair's Oscar Party Sunday, the couple got down to beauty business with makeup artist Charlotte Tilbury. But, it wasn't long until the actor, 44, stepped in to help his partner, 40, with her red carpet glam.

In a behind-the-scenes video shared to Tilbury's Instagram account, the pair are seen exchanging flirtatious banter as Long attempts to do Bosworth's eye makeup – just not in the traditional way.

"Darling, that's not for my brow, it's for my lip," the Blue Crush actress, wearing a white robe, says, as Long tries to shade in her eyebrows with the brand's Lip Cheat Liner in Pillow Talk.

"Please don't interrupt me darling. I'm unorthodox and I work in silence," Long jokingly shoots back, to which Bosworth replies, "But darling, I'm classical and I really need this to look put together."

According to Long, his technique is a trend. "This is all the rage now: lip liner on the eyebrows. Trust me, darling, trust me," he teased.

Both stars then broke out of character and shared a sweet kiss.

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Long and Bosworth attended the star-studded affair in Beverly Hills, California, where the Hollywood duo sparked engagement rumors when fans noticed Bosworth wearing a diamond ring on that finger.

Reps for Bosworth and Long did not immediately respond to PEOPLE's requests for comment.

The actors also dressed to the nines for their glamorous date night out. The Locksmith star wore a black-and-beige Monique Lhuillier gown with a sweetheart neckline and full skirt, while the Lady of the Manor director was clad in a traditional suit and tie.

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Last March, the couple were first linked after they were spotted together in Los Angeles. Long and Bosworth spent the previous year filming an unnamed project in Arkansas.

After seemingly confirming their relationship with PDA moments, the Clerk III actor opened up about their relationship on Chelsea Handler's Dear Chelsea podcast, saying that "being in love" is "such a wonderful feeling." They then broke the news on Instagram in May and June with separate posts.

In January, Long celebrated Bosworth's 40th birthday with a sweet Instagram tribute.

"She is 40! 🥳💛🎂" Long wrote in his post. "She is also the best part of my day, everyday - even when we're not together. She laughs with abandon. She makes me laugh the same - all the time. She sees beauty everywhere and in everyone. She thanks everyone - even when she's suffering, she's kind."

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RELATED: Kate Bosworth and Justin Long's Relationship Timeline

In return, Bosworth shared her own Instagram carousel dedicated to her beau and their endearing bond.

"You are my love and my light, my peace and my thrill. Thank you for holding my hand when we sleep. Thank you for tying my shoelaces when you notice they are undone. Thank you for making me laugh so hard I have to leave the room. Thank you for showing me what love is and for making this the best birthday ever 💛 xx," she captioned a series of adorable couple's snapshots.