Kutcher was seen partying at Madonna's annual post-Oscar party but his estranged wife Demi Moore was nowhere in the picture, reports radaronline.com.
Moore and Madonna are known as best of friends and the former even played a host at the 2011 Oscar bash.
A source present at the party said: "When Ashton walked in, it got the crowd buzzing. Madonna's never spoken about the split, but it's obvious she's sided with him over Demi."
"It was kind of shocking as Demi has even hosted the party with Madonna in the past, so it's even more of a mega snub. Madonna clearly loves Ashton though, they were dancing together a lot throughout the night and flirting up a storm," the source added.
Kutcher and Moore parted ways in 2011 after he was caught cheating on their sixth wedding anniversary.
Photos: Varun Dhawan and Alia Bhatt at studio in Bandra
Photos: Katrina Kaif, Shamita Shetty at Mumbai airport
Photos: Varun Dhawan, Alia Bhatt promote 'Badri...' on 'Dil Hai Hindustani'
In pictures: 15 facts about kissing that will surprise you
Photos: Shahid Kapoor and Mira Rajput at cafe in Bandra