Olivia Wilde all partied out after son Otis' 1st birthday

Olivia Wilde took a break from promoting her new documentary to hold a special first birthday party for her son Otis on Monday. The actress, who is engaged to Horrible Bosses star Jason Sudeikis, shared a snap from the party's aftermath with her Instagram followers on Monday night.

The image shows the star sprawled out on a huge stuffed animal, clearly exhausted after celebrating her little boy's special day.

"One year old birthday party semi-survivor," she captioned the image.

One year old birthday party semi-survivor.

A photo posted by Olivia Wilde (@oliviawilde) on

Speaking at the Tribeca Film Festival on Tuesday, Olivia said she felt "overwhelmed with happiness" after the celebrations.

"Oh yes my Birth-Day! Labour day as my mother-in-law calls it!" she told E! News. "We had an awesome celebration and especially in the midst of bringing Body Team 12 to the festival, I felt even more fortunate to be able to celebrate with Otis and be able to allow him to have this happy, happy day.

"I just feel so lucky and I am so overwhelmed with happiness."

The 31-year-old also revealed that her son is yet to say his first word: "He is working on it! He is really working on it!"

My kind of party.

A photo posted by Olivia Wilde (@oliviawilde) on

House star Olivia is clearly loving her new role as a mother, and gave fans a rare glimpse at her home life with Otis in an adorable photo posted to Instagram at the beginning of April.

"My kind of party," she wrote alongside the image, which showed her on all fours and grinning next to her little one.

It was the first photo Olivia shared of the tot since July. He appears to working on his walking skills too, even if he still needs a little support by holding on to the furniture.

Olivia's fiancé Jason has previously spoken proudly of Otis, and credited his "real cute" looks to his mother.

"He smiles a lot. I would say any looks he's got going – I feel like he's a real cute little guy – that's Olivia's doing."